Chemical Reactions: Chp 8

Describing Chemical Change: To understand chemical reactions we need to describe them in writing.

Describing a Chemical Change: Chemical reaction = one or more substances change into one or more new substances

Describing Chemical Change: Reactants vs. Products Reactants = those substances that are reacting or changing Products = those substances that are being formed from the reactants

Describing Chemical Change: In writing a chemical reaction, an arrow is used to separate the reactants from the products The arrow ( ) = yields, gives or reacts to produce

Describing Chemical Change Remember: All chemical reactions must follow the law of conservation of matter What is this law?

Describing Chemical Change: Chemical equations: using chemical formulas to describe in writing a chemical reaction The arrow separates the formulas of the reactants from the formulas of the products

Describing Chemical Change: Skeleton equation: Does not indicate relative amounts Shows just the formulas of the reactants and products Example: Fe + O2 Fe2O3

Describing Chemical Change: You can indicate the state of each substance by using symbols to represent solid (s), liquid (l), gas (g) and aqueous (aq) Example: Fe(s) + O2(g) Fe2O3(s)

Describing Chemical Change: Catalyst ? A substance that speeds up the rate of a reaction but is not used up in the reaction

Balancing Chemical Equations: If there is no indication of the quantity of reactants and products in a equation, it is unbalanced

Balancing Chemical Equations: Balanced equations usually contain coefficients: Coefficients = numbers placed in front of the symbols for the respective parts

Balancing Chemical Equations: Balanced chemical equation = has the same number of atoms of each elements on each side of the equation

Balancing Chemical Equations: Example: C(s) + O2(g) CO2(g) Each side of the equation has the same number of carbon and oxygen atoms The equation is balanced

Balancing Chemical Equations: Rules: page 208

Balancing Chemical Equations: Additional rules: 1. Solve the more complicated compounds first 2. Any polyatomic ions present on each side of the equation count as one unit 3. Solve the single elements last