Chapter 18 Reaction Rates and Equilibrium 18.1 Rates of Reaction

Chapter 18 Reaction Rates and Equilibrium 18.1 Rates of Reaction
18.2 The Progress of Chemical Reactions 18.3 Reversible Reactions and Equilibrium 18.4 Solubility Equilibrium 18.5 Free Energy and Entropy Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Describing Reaction Rates
* The speed of chemical reactions can vary from very fast to extremely slow. When you strike a match, it erupts into flame almost instantly and burns quickly. Millions of years were required for plants buried beneath Earth’s surface to be converted to coal. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The rate of a chemical reaction, or the reaction rate, is expressed as the change in the amount of reactant or product per unit time. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Collision Theory A model called collision theory is used to relate the properties of particles to the rates of chemical reactions. Collision theory: atoms, ions, and molecules react to form products when they collide if they have enough kinetic energy (speed). Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Collision Theory A model called collision theory is used to relate the properties of particles to the rates of chemical reactions. Collision theory: atoms, ions, and molecules react to form products when they collide if they have enough kinetic energy (speed). Particles that do not have enough energy to react bounce apart unchanged. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The minimum energy needed to react is called the activation energy. Activation energy is like a barrier that reactants must cross before products can form. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

When two reactant particles collide, they may form an activated complex. An activated complex is an unstable arrangement of atoms that forms for a moment at the peak of the activation-energy barrier. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

When two reactant particles collide, they may form an activated complex. An activated complex is an unstable arrangement of atoms that forms for a moment at the peak of the activation-energy barrier. The activated complex forms only if the colliding particles have enough energy and if the atoms are oriented properly. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

When two reactant particles collide, they may form an activated complex. The lifetime of an activated complex is typically about seconds. Its brief existence ends with the reformation of the reactants or with the formation of products. The activated complex is sometimes called the transition state. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Interpret Graphs Remember: An endothermic reaction absorbs heat, and an exothermic reaction releases heat. The activation-energy barrier must be crossed before reactants are converted to products. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Collision theory explains why some reactions are extremely slow at room temperature. Carbon and oxygen react when charcoal burns, but the reaction has a high activation energy. The O—O and C—C bonds must be broken to form the activated complex. At room temperature, the collisions of oxygen and carbon molecules are not energetic enough to break the bonds. Thus, the reaction rate of carbon with oxygen at room temperature is essentially zero. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What factors determines whether a molecular collision results in a reaction?
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What factors determines whether a molecular collision results in a reaction?
The molecules must collide oriented properly and with enough energy in order to react. The minimum amount of energy needed is called the activation energy. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Factors Affecting Reaction Rates
By varying conditions, you can modify the rate of almost any reaction. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Factors that can affect the rate of a chemical reaction are temperature, concentration, particle size, and use of a catalyst. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Concentration The number of particles in a given volume affects the rate at which reactions occur. Cramming more particles into a fixed volume increases the concentration of reactants, and, thus, the frequency of collision. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Concentration The number of particles in a given volume affects the rate at which reactions occur. Cramming more particles into a fixed volume increases the concentration of reactants, and, thus, the frequency of collision. Increased collision frequency leads to a higher reaction rate. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Particle Size The surface area of reactants will affect the rate of a reaction. Crushing into a powder increases surface area speeding up the reaction. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Particle Size Another way to increase the surface area of a solid is to dissolve them. In a solution, particles are separated and more accessible to other reactants. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Catalysts Increasing the temperature is not always the best way to increase the rate of a reaction. A catalyst is often better. Recall that a catalyst is a substance that increases the rate of a reaction without being used up during the reaction. Catalysts permit reactions to proceed along a lower energy path. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Interpret Graphs The activation-energy barrier for the catalyzed reaction is lower than that of the uncatalyzed reaction. When the barrier is lower, a greater amount of reactants have the energy to form products within a given time. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Catalysts The rate of reaction of hydrogen and oxygen at room temperature is negligible. But with a small amount of platinum (Pt) as a catalyst, the reaction is rapid. 2H2(g) + O2(g) H2O(ℓ) Pt Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Catalysts At normal body temperature (37C), reactions in the body would be too slow without catalysts. The catalysts that increase the rates of biological reactions are called enzymes. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Catalysts At normal body temperature (37C), reactions in the body would be too slow without catalysts. The catalysts that increase the rates of biological reactions are called enzymes. When you eat a meal containing protein, enzymes in your digestive tract help break down the protein molecules in a few hours. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Inhibitors An inhibitor is a substance that interferes with the action of a catalyst. Some inhibitors work by reacting with, or “poisoning,” the catalyst itself. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Inhibitors An inhibitor is a substance that interferes with the action of a catalyst. Some inhibitors work by reacting with, or “poisoning,” the catalyst itself. Thus, the inhibitor reduces the amount of catalyst available for a reaction. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Inhibitors An inhibitor is a substance that interferes with the action of a catalyst. Some inhibitors work by reacting with, or “poisoning,” the catalyst itself. Thus, the inhibitor reduces the amount of catalyst available for a reaction. Reactions slow or even stop when a catalyst is poisoned. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

A. Catalyst concentration B. Concentration C. Temperature
Which of the following factors could be increased in order to decrease a reaction rate? A. Catalyst concentration B. Concentration C. Temperature D. Particle size Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Which of the following factors could be increased in order to decrease a reaction rate?
A. Catalyst concentration B. Concentration C. Temperature D. Particle size Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

How can you quantify the amount of sand in a sand sculpture?
CHEMISTRY & YOU How can you quantify the amount of sand in a sand sculpture? You could measure the amount of sand in a sculpture by counting the grains of sand. Is there an easier way to measure the amount of sand? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Chemistry is a quantitative science.
Measuring Matter Chemistry is a quantitative science. In your study of chemistry, you will solve problems and perform chemical calculations. To solve these and other problems, you will have to be able to measure the amount of matter you have. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Things can be measured in three different ways.
Measuring Matter Things can be measured in three different ways. At a fruit stand, apples are often sold by the count. In a supermarket, you usually buy apples by weight or mass. At an orchard, you can buy apples by volume. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

How can you convert among the count, mass, and volume of something?
Measuring Matter Measuring Matter How can you convert among the count, mass, and volume of something? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Measuring Matter Knowing how count, mass, and volume are relate to a common unit allows you to convert among these units. Based on the relationship, you could calculate the mass of a bushel of apples or the mass of 90 average-sized apples using the following conversion factors: 12 apples 1 dozen apples 2.0 kg apples 0.20 bushel apples Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Finding Mass from a Count
Sample Problem Finding Mass from a Count What is the mass of 75 average-sized apples if 1 dozen of the apples has a mass of 2.0 kg? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Analyze Solve for the unknown.
Sample Problem Analyze Solve for the unknown. 1 First identify the sequence of conversions needed to perform the calculation. number of apples ↓ dozens of apples mass of apples Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Analyze List the knowns and the unknown.
Sample Problem Analyze List the knowns and the unknown. 1 Use dimensional analysis to convert the number of apples to the mass of apples. KNOWNS number of apples = 75 apples 12 apples = 1 dozen apples 1 dozen apples = 2.0 kg apples UNKNOWN mass of 75 apples = ? kg Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Calculate Solve for the unknown.
Sample Problem Calculate Solve for the unknown. 2 Write the conversion factor to convert from number of apples to dozens of apples. 12 apples 1 dozen apples Write the conversion factor to convert from dozens of apples to mass of apples. 1 dozen apples 2.0 kg apples Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Calculate Solve for the unknown. 2 Multiply the number of apples by these two conversion factors to get the answer in kilograms. 75 apples 1 × 12 apples 1 dozen apples 2.0 kg apples × = 12.5 kg of apples The units apples and dozen apples cancel, so the answer has the unit kg. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Evaluate Does the result make sense?
Sample Problem Evaluate Does the result make sense? 3 A dozen apples has a mass of 2.0 kg, and 75 apples is less than 7 dozen apples, so the mass should be less than 14 kg of apples (7 dozen x 2.0 kg/dozen). Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Matter is composed of atoms, molecules, and ions.
What Is a Mole? Matter is composed of atoms, molecules, and ions. These particles are much, much smaller than grains of sand, and an extremely large number of them are in a small sample of a substance. Obviously, counting particles one by one is not practical and impossible. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

What Is a Mole? Counting with Moles The mole allows chemists to count the number of representative particles in a substance. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

What Is a Mole? Counting with Moles A mole (mol) is the SI unit for measuring the amount of a substance. One mole is 6.02 × 1023 representative particles of that substance. The number, 6.02 × 1023, is called Avogadro’s number. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

The Size of a Mole What Is a Mole?
If you had Avogadro’s number of animal-moles… The mass would be equal to more than 60 times the combined mass of Earth’s oceans. If spread over the entire surface of Earth, it would form a layer more than 8 million animal-moles thick. If lined up end-to-end, it would stretch from Earth to the nearest star, Proxima Centauri, more than two million times. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

What Is a Mole? Counting with Moles The term representative particle refers to the particle type present in a substance. (atoms, molecules, or formula units) The representative particle of most elements is the atom. Iron is composed of iron atoms. Helium is composed of helium atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

What Is a Mole? Counting with Moles Seven elements normally exist as diatomic molecules (H2, N2, O2, F2, Cℓ2, Br2, and I2). The representative particle of these 7 elements and of ALL molecular compounds is the molecule. The molecular compounds water (H2O) and sulfur dioxide (SO2) are composed of H2O and SO2 molecules, respectively. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

For ionic compounds the representative particle is the formula unit.
What Is a Mole? Counting with Moles For ionic compounds the representative particle is the formula unit. For calcium chloride that would be CaCℓ2. For lead(II) nitrate that would be Pb(NO3)2. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Representative Particles and Moles
Interpret Data Counting with Moles The table below summarizes the relationship between representative particles and moles of substances. Representative Particles and Moles Substance Representative particle Chemical formula Representative particles in 1.00 mol Copper Atom Cu 6.02 × 1023 Atomic nitrogen N Nitrogen gas Molecule N2 Water H2O Calcium ion Ion Ca2+ Calcium fluoride Formula unit CaF2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Converting Between Number of Particles and Moles
What Is a Mole? Converting Between Number of Particles and Moles The relationship 1 mol = 6.02 × 1023 representative particles is the basis for the following conversion factors that you can use. 1 mol 6.02 × 1023 representative particles or 6.02 × 1023 representative particles 1 mol Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Converting Number of Atoms to Moles
Sample Problem Converting Number of Atoms to Moles Magnesium is a light metal used in the manufacture of aircraft, automobile wheels, and tools. How many moles of magnesium is 1.25 × 1023 atoms of magnesium? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Analyze List the known and the unknown.
Sample Problem Analyze List the known and the unknown. 1 The desired conversion is atoms → moles. KNOWN number of atoms = 1.25 × 1023 atoms Mg UNKNOWN moles = ? mol Mg Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Calculate Solve for the unknown. 2 First state the relationship between moles and number of representative particles. 1 mol Mg = 6.02 × 1023 atoms Mg Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Calculate Solve for the unknown. 2 Write the conversion factors you get based on this relationship. 1 mol Mg 6.02 × 1023 atoms Mg or Identify the conversion factor needed to convert from atoms to moles. 6.02 × 1023 atoms Mg 1 mol Mg Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

= 0.208 mol Mg = 2.08 x 10-1 mol Mg Calculate Solve for the unknown.
Sample Problem Calculate Solve for the unknown. 2 Multiply the number of atoms of Mg by the conversion factor. 6.02 × 1023 atoms Mg 1 mol Mg 1.25 × 1023 atoms Mg 1 × = mol Mg = 2.08 x 10-1 mol Mg Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Evaluate Does the result make sense? 3 The given number of atoms (1.25 × 1023) is less than one-fourth of Avogadro’s number (6.02 × 1023), so the answer should be less than one-fourth (0.25) mol of atoms. The answer should have three significant figures. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

What Is a Mole? Converting Between Number of Particles and Moles Suppose you want to determine how many atoms are in a mole of a compound. To do this, you must know how many atoms are in a representative particle of the compound. This number is determined from the chemical formula. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

What Is a Mole? Converting Between Number of Particles and Moles Carbon dioxide (CO2): the subscripts show that one molecule of carbon dioxide is composed of 3 atoms: one (1) carbon atom and two (2) oxygen atoms. A mole of carbon dioxide contains Avogadro’s number of CO2 molecules. Each molecule contains 3 atoms, so a mole of carbon dioxide contains 3 times Avogadro’s number of atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Converting Moles to Number of Atoms
Sample Problem Converting Moles to Number of Atoms Propane is a gas used for cooking and heating. How many atoms are in 1.12 mol of propane (C3H8)? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

moles → molecules → atoms.
Sample Problem Analyze List the knowns and the unknown. 1 The desired conversion is: moles → molecules → atoms. KNOWNS number of moles = 1.12 mol C3H8 1 mol C3H8 = 6.02 × 1023 molecules C3H8 1 molecule C3H8 = 11 atoms (3 carbon atoms and 8 hydrogen atoms) UNKNOWN number of atoms = ? atoms Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Calculate Solve for the unknown. 2 First write the conversion factor to convert from moles to molecules. 6.02 × 1023 molecules C3H8 1 mol C3H8 Remember to write the conversion factors so that the unit in the denominator cancels the unit in the numerator of the previous factor. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Calculate Solve for the unknown. 2 Write the conversion factor to convert from molecules to atoms. 11 atoms 1 molecule C3H8 There are 3 atoms of carbon and 8 atoms of hydrogen in 1 molecule of propane. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem 10.3 Calculate Solve for the unknown. 2 Multiply the moles of C3H8 by the conversion factors. 1 molecule C3H8 1.12 mol C3H8 1 6.02 × 1023 molecules C3H8 1 mol C3H8 × 11 atoms × = 7.42 × 1024 atoms Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem 10.3 Evaluate Does the result make sense? 3 There are 11 atoms in each molecule of propane and more than 2 mol of propane, so the answer should be more than 20 times Avogadro’s number of propane molecules. The answer has three significant figures, based on the three significant figures in the given measurement. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

How is a mole similar to a dozen?
Both “mole” and “dozen” are quantities made of a specified number of “representative particles.” They both refer to multiple objects or particles that are now being thought of as a single object or particle with multiple parts. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

The Mass of a Mole of an Element
Molar Mass The Mass of a Mole of an Element The atomic mass of an element expressed in grams is the mass of a mole of the element. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

The Mass of a Mole of an Element
Molar Mass The Mass of a Mole of an Element The atomic mass of an element expressed in grams is the mass of a mole of the element. The mass of a mole of an element is its molar mass. For carbon, the molar mass is 12.0 g. For atomic hydrogen, the molar mass is 1.0 g. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

The Mass of a Mole of a Compound
Molar Mass The Mass of a Mole of a Compound To calculate the molar mass of a compound, find the number of grams of each element in one mole of the compound. Then add the masses of the elements in the compound. This method for calculating molar mass applies to any compound, molecular or ionic. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Molar Mass The Mass of a Mole of a Compound To find the mass of a mole of a compound, you must know the formula of the compound. A molecule of SO3 is composed of one atom of sulfur and three atoms of oxygen. You can calculate the mass of a molecule of SO3 by adding the atomic masses of the atoms making up the molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Molar Mass The Mass of a Mole of a Compound From the periodic table, the atomic mass of sulfur (S) is 32.1 amu. The mass of three atoms of oxygen is three times the atomic mass of a single oxygen atom (O): 3 × 16.0 amu = 48.0 amu. The molecular mass of SO3 is 32.1 amu amu = 80.1 amu. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Molar Mass The Mass of a Mole of a Compound Now substitute the unit grams for atomic mass units (amu) to find the molar mass of SO3. 1 mol of SO3 has a mass of 80.1 g. This is the mass of 6.02 x 1023 molecules of SO3. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Finding the Molar Mass of a Compound
Sample Problem Finding the Molar Mass of a Compound The decomposition of hydrogen peroxide (H2O2) provides sufficient energy to launch a rocket. What is the molar mass of hydrogen peroxide? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Analyze List the knowns and the unknown.
Sample Problem Analyze List the knowns and the unknown. 1 Convert moles of atoms to grams by using conversion factors (g/mol) based on the molar mass of each element. The sum of the masses of the elements is the molar mass. KNOWNS molecular formula = H2O2 mass of 1 mol H = 1.0 g H mass of 1 mol O = 16.0 g O UNKNOWN molar mass = ? g/mol Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Calculate Solve for the unknown. 2 Convert moles of hydrogen and oxygen to grams of hydrogen and oxygen. 2 mol H 1 = 2.0 g H 1.0 g H 1 mol H 2 mol O = 32.0 g O 16.0 g O 1 mol O × × One mole of H2O2 has 2 mol of H atoms and 2 mol of O atoms, so multiply the molar mass of each element by 2. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

molar mass of H2O2 = 34.0 g/mol Calculate Solve for the unknown.
Sample Problem Calculate Solve for the unknown. 2 Add the results. mass of 1 mol H2O2 = 2.0 g H g O molar mass of H2O2 = 34.0 g/mol Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Sample Problem Evaluate Does the result make sense? 3 The answer is the sum of two times the molar mass of hydrogen and oxygen (17.0 g). The answer is expressed to the tenths place because the numbers being added are expressed to the tenths place. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Complete the following analogy:
Molar mass is to a mole of a substance as atomic/molecular mass is to one atom or molecule of a substance. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Chapter 18 Reaction Rates and Equilibrium 18.1 Rates of Reaction

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