Chapter 19
Chemical Reactions
1. Chemical Changes
a. Lavoisier and the Conservation of Mass
i. chemical reaction-change in which one or more substances are converted into
new substances
ii. reactants-starting substances that combine or change
iii. products-new substances that are produced
iv. Antoine Lavoisier-experimented with mercury (II) oxide and heat and found that
the products (liquid mercury and oxygen gas) equaled mass of reactants
v. Law of conservation of mass-the total starting mass of all reactants is equal to the
total final mass of all products
b. Writing Equations
i. chemical equation-a way to describe a chemical reaction using chemical formulas
and other symbols
1. example: 2NiCl2(l) + 2NaOH(aq) - > Ni(OH)2(s) + 2NaCl(aq)
reactants
yields
products
2. states of matter- (s) solid; (l) liquid; (g) gas; (aq) aqueous
c.
Coefficients
i. Coefficients are numbers which represent the number of units of each substance
in a reaction (placed in front of formulas or symbols in equation).
ii. Atoms can be rearranged but never destroyed in a chemical reaction
d. Balancing Equations
i. Choosing coefficients-involves changing coefficients in a reactions in order to
achieve a balanced chemical equation.
ii. Try your balancing act
1. Write the equation using symbols and formulas.
2. Count the atoms in reactants and products.
3. Choose coefficients that balance the equation.
4. Recheck the numbers of each atom on each side of the equation and
adjust coefficients again if necessary
2. Classifying Chemical Reactions
a. Types of Reactions
i. Combustion reaction-a substance reacts with oxygen to form heat and light.
ii. Synthesis reaction-two or more combine to form another substance:
1. A +B -> C
2. H2(g) + Cl2(g) -> 2HCl(g)
iii. Decomposition reaction -one substance breaks down into two or more
1. substances: AB->A+B
2. 2H2O2(l) -> O2(g) + 2H2O(l)
iv. Single-displacement reaction-one element replaces another one in a compound:
1. A + BC -> AC + B
2. Cu(s) + 2AgNO3(aq) -> Cu(NO3)2(aq) + 2Ag(s)
v. Double-displacement reaction-results if a precipitate, water, or gas forms when
two ionic compounds in solution are combined.
1. AB+ CD -> AD + CB
2. 2NaOH(aq) + CuCl2(aq) -> Cu(OH)2(s) + 2NaCl(aq)
3. Chemical Reactions and Energy
a. Chemical reactions - energy exchanges
b. Breaking chemical bonds requires energy
c. Forming chemical bonds releases energy
d. Exothermic reaction-energy is given off in the form of thermal energy
e. Endothermic reaction-energy is required in the form of thermal energy
4. Reaction Rates and Equilibrium
a. Reaction rate- the rate at which reactants change into products
b. Factors affecting reaction rates (collision model states that atoms, ions, and molecules
must collide in order to react)
i. Increasing Temperature
ii. Increase Concentration
iii. Increasing Surface Area
iv. Adding a catalyst-speeds up a chemical reaction without being permanently
changed
v. inhibitor-prevents or slows down a chemical reaction
Chapter 19 Vocabulary
Balanced chemical equation - Chemical equation with the same number of atoms of each element on both
sides of the equation
Catalyst - Substance that speeds up a chemical reaction without being permanently changed itself
Chemical equation - Shorthand method used to describe chemical reactions using chemical formulas and
other symbols
Chemical reaction - Process in which one or more substances are changed into new substances
Coefficient - Number in a chemical equation that represents the number of units of each substance taking
part in a chemical reaction
Collision model - Explains why certain factors affect reaction rates, states that particles must collide in
order to react
Combustion reaction - A type of chemical reaction that occurs when a substance reacts with oxygen to
produce energy in the form of heat and light
Decomposition reaction - Chemical reaction in which one substance breaks down into two or more
substances
Double-displacement reaction - Reaction in which two ionic compounds in solution are combined, can
produce a precipitate, water, or a gas
Endothermic reaction - Chemical reaction that requires thermal energy in order to proceed
Equilibrium - State in which forward and reverse reactions or processes occur at equal rates
Exothermic reaction - Chemical reaction in which energy is primarily given off in the form of thermal
energy
Inhibitor - Substance that slows down a chemical reaction or prevents it from occurring by combining
with a reactant
Le Hotelier’s principle -States that if a stress is applied to a reaction at equilibrium, the reaction shifts in
the direction opposite of the stress
Molar mass - The mass in grams of one mole of a substance
Mole - SI unit for quantity equal to 6.022 × 10^23 units of that substance
Oxidation -The loss of electrons from the atoms of a substance in a chemical reaction
Precipitate - Insoluble compound that is formed in a solution during a double-displacement reaction
Product - In a chemical reaction, the new substance or substances formed
Reactant - In a chemical reaction, the substance that reacts
Reaction rate - The rate at which reactants change into products in a chemical reaction
Reduction - The gain of electrons by the atoms of a substance in a chemical reaction
Reversible reaction - A reaction that can proceed in both the forward and the reverse directions
Single-displacement reaction - Chemical reaction in which one element replaces another element in a
compound
Synthesis reaction - Chemical reaction in which two or more substances combine to form a different
substance