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.

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

Using Equations to Represent Reactions Reactants _______ into products Reactants  Products ______ + ______  ______________ C + O2  CO2 Chemical ________ is a representation of a chemical reaction in which the reactants and products are expressed as _________. “Carbon and oxygen react and form carbon dioxide”

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 ______________ ______. The law of conservation of mass states that mass is neither ______ nor ________ in a chemical reaction Whether you burn one carbon atom or six carbon atoms, the equation used to describe the reaction is the same.

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

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

Math Practice 1.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

Balancing Rules _________- the numbers that appear ________ the formulas. In the unbalanced equation above, the coefficients are understood to be___ When you change a coefficient, you ______ the amount of that reactant or product represented in the chemical equation. As you balance equations, you should ______ change the ____________ in a formula

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 _________ reactions, ___________ reactions, ______________ reactions, ___________________ reactions, and ____________ reactions.

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

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

Single Replacement +  + Ex: Cu + 2Ag(NO3)  2Ag + Cu(NO3) +  + Ex: Cu + 2Ag(NO3)  2Ag + Cu(NO3) K + 2H2O  H2 + 2KOH One element takes the ____ 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.

Double Replacement +  + Ex: Pb(NO3) 2  PbI2 + 2KNO3 +  + Ex: Pb(NO3) 2  PbI2 + 2KNO3 CaCO3 + 2HCl  CaCl2 + H2CO3 Two different compounds exchange ___________ 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.

Combustion Ex: CH4 + 2O2  CO2 + H2O A substance reacts _____ with ______, often producing heat and light. Ex: 2H2 + O2  2H2O Notice that you could also classify this reaction as the ________ of water. The classifications for chemical reactions sometimes _________ A Bunsen burner generates heat and light by the combustion of natural gas.

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

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

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

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

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

Factors Affecting Reaction Rates 5. _______- A substance that affects the reaction rate without being used up in the reaction. Catalysts are used so reactions can occur at ________ temperatures. Catalysts are written _____ the arrow. Energy is needed to start breaking the chemical bonds. This is called _________________. Catalysts lower that energy needed by providing a ________ 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.