Chapter 7 Chemical Reactions Burning is an example of a chemical reaction. When charcoal burns, the carbon in the charcoal reacts with oxygen in the air to produce carbon dioxide and heat. Girl mixing chemicals: https://youtu.be/AhG1nv1T6ZA Mr Bean: https://www.youtube.com/watch?v=6aK2CKrdjbE Chemical Reaction compilation: https://www.youtube.com/watch?v=8TPnns-5UxA Chapter 7 Chemical Reactions

7.1 Describing Reactions What are Chemical Equations? A chemical reaction tells you the substances present before and after a reaction Reactants-substances that undergo change Products-The new substances formed as a result of that change

Using Equations to Represent Reactions Reactants change into products Reactants  Products Carbon + Oxygen  Carbon Dioxide C + O2  CO2 Chemical Equation is a representation of a chemical reaction in which the reactants and products are expressed as formulas. “Carbon and oxygen react and form carbon dioxide”

Practice yourself Label the reactants and products for each: 1. Blue + Yellow  Green 2. Gasoline + Fire  Heat + Smoke 3. Gatorade  K+ ions + Na+ ions + Sugar Reactants: Products: Reactants: Products: Reactants: Products:

Atoms are not created OR destroyed during a reaction Conservation of Mass Mass of the products is always ___________ to the mass of the reactants. French chemist Antoine Lavoisier (1743–1794), developed the law of conservation of mass. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction Atoms are not created OR destroyed during a reaction Whether you burn one carbon atom or six carbon atoms, the equation used to describe the reaction is the same.

Conservation of Mass 6 12 18

Parts of an equation Definitions: Subscript: Coefficient: Yield sign: 2C + 2S2  2CS2 Definitions: Subscript: Coefficient: Yield sign: Reactants: Products:

Molar Mass (abbrev MM) What is a Mole? Basically, a mole is a unit of something Molar Mass is the mass of the parts of a molecule The same mass that’s on the periodic table Ex1: Molar Mass of Sodium (Na) is 23 Ex2: Molar Mass of Chlorine is 35.45 Ex3: MM of salt (NaCl) MUST be broken down into Na and Cl - The MM of Na is 23 - The MM of Cl is 35.45 - The combined mass of NaCl is 58.45 Add 23 + 35.45

Now… use Molar Mass to balance an Equation 1. 2C + 2S2  2CS2 2. 2 O2 + P  PO4 3. NH4 + KCl  KH3 + HCl

Molar Mass… Continued CO2 NaNH4 Ba3(PO4)2

Balancing Equations In order to show mass is conserved, the chemical equation must be balanced. N2H4 + O2  N2 + _ 2_ H2O N 2 N 2 H 4 H 2 x_2_ =4 O 2 O 1 x _2_=2

Chemical Equations Ca + Cl  CaCl2 Ca= Ca= Cl= Cl= Steps for solving Chemical Equations Step 1: Assume the equation is WRONG Step 2: Write the # of atoms for each “side” of the equation Step 3: Make adjustments to the “sides” to make sure that the masses balance out Ca + Cl  CaCl2 Ca= Ca= Cl= Cl=

Now Slightly harder… I2 + NaCl  NaI + Cl2 I = I = Na = Na = Cl = Cl =

To balance a chemical equation, first count the atoms on each side of the equation.

Balancing Rules Coefficients- the numbers that appear before the formulas. In the unbalanced equation above, the coefficients are understood to be 1__ When you change a coefficient, you change the amount of that reactant or product represented in the chemical equation. As you balance equations, you should never change the subscripts in a formula

Practice Hydrogen chloride, or HCl, is an important industrial chemical. Write a balanced equation for the production of hydrogen chloride from hydrogen and chlorine. 2. Balance the following chemical equations. 3. Ethylene, C2H4, burns in the presence of oxygen to produce carbon dioxide and water vapor. Write a balanced equation for this reaction

7.2 Types of Reactions Just as you can classify matter into different types, you can classify chemical reactions into different types Some general types of chemical reactions are: Synthesis reactions Decomposition reactions Single-replacement reactions Double-replacement reactions Combustion reactions

1. Synthesis (Combination) A + B  AB Ex: 2Na + Cl2 2 NaCl 2H2 + O2  2H2O Two or more substances react to form a single substance. Sodium metal reacts vigorously with chlorine to form sodium chloride, NaCl

2. Decomposition AB  A + B Ex: 2H2O  2H2 + O2 CaCO3  CaO + CO2 A compound breaks down into two or more simpler substances.

3. Single Replacement AB + C  A + BC Ex: Cu + 2Ag(NO3)  2Ag + Cu(NO3) K + 2H2O  H2 + 2KOH One element takes the place of another element in a compound Potassium reacts with water in a single-replacement reaction that produces hydrogen gas and potassium hydroxide. A single-replacement reaction occurs when copper wire is submerged in a solution of silver nitrate.

4. Double Replacement AB + CD  AD + CB Ex: Pb(NO3) 2 + 2KI  PbI2 + 2KNO3 CaCO3 + 2HCl  CaCl2 + H2CO3 Two different compounds exchange positive ions and form two new compounds. When potassium iodide solution is poured into a solution of lead(II) nitrate, a double-replacement reaction takes place. Lead(II) iodide forms as a yellow precipitate.

5. Combustion Ex: CH4 + 2O2  CO2 + 2 H2O Ex: 2H2 + O2  2H2O A substance reacts rapidly with oxygen, often producing heat and light. Ex: 2H2 + O2  2H2O Notice that you could also classify this reaction as the synthesis of water. The classifications for chemical reactions sometimes overlap A Bunsen burner generates heat and light by the combustion of natural gas. Practice on worksheet 8 …… Continue by finishing Page 6 and 7

Summary of Reaction Types

7.4 Reaction Rates Reaction Rates- Rate at which reactants change into products over time. Reaction rates tell you how fast a reaction is going. That is, how fast the reactants are being consumed, how fast the products are being formed, or how fast energy is being absorbed or released

Next Topic… Factors that affect the SPEED of reactions

Factors Affecting Reaction Rates 1. Temperature - Generally, an increase in temperature will increase the reaction rate. Ex: You store milk in a refrigerator to slow down the reactions that cause the milk to spoil Increasing the temperature of a substance causes its particles to move faster, on average. Particles that move faster are both more likely to collide and more likely to react. If the number of collisions that produce reactions increases, then the reaction rate increases

Factors Affecting Reaction Rates 2. Surface Area - An increase in surface area increases the exposure of reactants to one another. The smaller the particle size of a given mass, the larger is its surface area. An increase in surface area increases the exposure of reactants to one another. The greater this exposure, the more collisions there are that involve reacting particles. With more collisions, more particles will react. This is why increasing the surface area of a reactant tends to increase the reaction rate.

Factors Affecting Reaction Rates 3. Stirring - Stirring the reactants will generally increase the reaction rate. Collisions between the particles of the reactants are more likely to happen Ex: A washing machine speeds up the reaction by stirring the contents back and forth

Factors Affecting Reaction Rates 4. Concentration - The more reacting particles present, the more opportunities there are for collisions involving particles. For gases, concentration changes with pressure. The greater the pressure of a gaseous reactant, the greater is its concentration, and the faster is the reaction rate. The dye solution in the left beaker is more concentrated than the solution in the right. Increasing the concentration of the dye increases the rate of color change in the material.

Factors Affecting Reaction Rates 5. Catalysts - A substance that affects the reaction rate without being used up in the reaction. Catalysts are used so reactions can occur at lower temperatures. Catalysts are written above the arrow. Energy is needed to start breaking the chemical bonds. This is called activation energy. Catalysts lower that energy needed by providing a surface on which the reacting particles can come together.

How a Catalyst Works The graph shows how a catalyst lowers the amount of energy required for effective collisions between reacting particles.

Molar Mass Quiz Directions: Show all work, include unit of measurement, and circle final answer.   H2O (NH3)4 C2H4O2 K2Cr2O7

Do Now What is the molar mass of: C6H12O6 (a sugar molecule) O3 (An Ozone molecule) 2. Using the terms in the equation below, explain how carbon is the same on each side of the equation… as the Law of Conservation of Mass says. Wood + O2 + spark = ashes + CO2

Do Now ___ Fe2O3 + ___C  ___Fe + ___CO2 _____NO + ____O2  _____NO2 Balance the following reactions: ___ Fe2O3 + ___C  ___Fe + ___CO2 _____NO + ____O2  _____NO2 ____CO2 + ____H2  ___CO + ___H2O