Chapter 17 Chemical Reactions

Chemical Formulas and Equations

Matter can change physically or chemically; a process that produces a chemical change is a chemical reaction (pg. 496). A chemical equation is a shorthand form of what reactants are used and what products are formed in a chemical reaction.

1. Some equations use words or chemical names to identify reactants and products. 2. Chemical formulas represent chemical names of substances in a chemical equation. C. The mass of reactants and mass of products in a chemical reaction is always the same due to the law of conservation of mass.

D. Chemical equations are balanced when the number of atoms is the same on each side of the equation pg. 497). E. Energy is released or absorbed during a chemical reaction. 1.When reactions release energy (exothermic reactions), the products have bonds with less energy than those of the reactants.

2. When reactions absorb energy (endothermic reaction), the reactants are more stable and their bonds have less energy than those of the products. 3. Heat energy may be absorbed or released; the rate of heat release can be rapid or slow. 4. The word energy can be written in a chemical equation as a reactant or a product (pg. 499).

Discussion Question A chemical equation is composed of what two items

Answer The reactants and the products

Rates of Chemical Reactions Section 2 Rates of Chemical Reactions

Different chemical reactions take different amounts of time. Activation energy – the amount of energy needed to start a chemical reaction. The rate of reaction measures how quickly a reactant is disappearing or how quickly a product is appearing.

1. Tells how quickly the amount of a substance changes per unit of time. 2. Importance in industry: the faster a product can be made, the lower its cost. 3. Temperature can change the rate of reaction. 4. Concentration, the amount of a substance present in a specific volume, affects the rate of reaction.

5. Particle size affects the speed of reaction. D 5. Particle size affects the speed of reaction. D. Inhibitor – a substance that slows down the rate of chemical reaction. E. Catalyst – A substance that speeds up a chemical reaction; enzymes are special protein molecules that act as catalysts in the body.

The Art of Balancing Equations Section 3

One of the most useful devices for communicating information related to chemical changes is the chemical equation.

be neither created nor destroyed For the purpose of equation balancing we say that energy can be neither created nor destroyed. Thus the number of atoms at the beginning of a reaction (reactants - left side of the equation) must equal the number of atoms at the end of the reaction (products - right side of the equation).

What Law Says This????

The Law of Conservation of Mass!

The subscripts in a correct formula tell the number of atoms in the one molecule in front of it. The coefficients (numbers in front of a formula) in a correctly balanced equation tell the number of molecules involved in a reaction.

Remember, you CANNOT change a subscript to balance the equation, nor can you add in new compounds.

Fe2(C2O4)3 ---> FeC2O4 + CO2 •When an equation is in parenthesis, the subscript is referring to ALL of the elements in the parenthesis. Fe2(C2O4)3 ---> FeC2O4 + CO2