Balancing chemical equations Chemical Reaction Reactant Product Chemical Equation Coefficient Point out Homework assignment

Chemical reactions are represented by balanced chemical equations.

Conservation of Mass The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction, it is conserved. The mass of the reactants equals the mass of the products. massreactants = massproducts

What are some examples of evidence of a chemical reaction? Chemical Reactions The process by which one or more substances are rearranged to form different substances is called a chemical reaction. What are some examples of evidence of a chemical reaction? Candle burning, baking soda and vinegar, burning woods, acids and bases. Evidence: color change, production of a gas, production of a precipitate, changes in size or shape

Representing Chemical Reactions Chemists use statements called equations to represent chemical reactions. Reactants: are the starting substances. Products: are the substances formed in the reaction. This table summarizes the symbols used in chemical equations. Copy the table into your notes

Representing Chemical Reactions (cont.) In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”. Skeleton equations use symbols and formulas to represent the reactants and products. Example: Al(s) + Br(l) → AlBr3(s) Skeleton equations lack information about how many atoms are involved in the reaction.

Representing Chemical Reactions (cont.) A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

Balancing Chemical Equations This figure shows the balanced equation for the reaction between aluminum and bromine.

N2 (g) + H2 (g) -------> NH3 (g) Balancing Chemical Equations (cont.) Subscripts describe the number of atoms present in one molecule. (Small numbers following elements/compounds). N2 (g) + H2 (g) -------> NH3 (g)  Coefficients are generally used for balancing the chemical equations in accordance with the law of conservation of mass. (Large numbers out in front of elements/compounds). N2 (g) + 3 H2 (g) -------> 2 NH3 (g) 

Balancing Chemical Equations (cont.)

Balancing Chemical Equations (cont.)

Balancing Chemical Equations (cont.)

Balancing Chemical Equations (cont.) The most fundamental law in chemistry is the law of conservation of mass. Balanced equations show this law.

Balancing Chemical Equations (cont.) COPY THIS CHART INTO YOUR NOTES Finish here with 7th

Balancing Chemical Equations (cont.) Two helpful hints Never start with balancing oxygen; you can get into a crazy never ending loop. If a polyatomic ion exists on both sides of the equation you can keep it together if balancing is giving you trouble. Polyatomic ions are on the back of the periodic table. Start here with 3rd and 5th

Balancing Chemical Equations (cont.) ___H2 + ___O2 → ___H2O

Balancing Chemical Equations (cont.) ___Fe + ___H2O → ___H2 + ___Fe2O3

Balancing Chemical Equations (cont.) ___C2H2 + ___O2 → ___H2O + ___CO2

Balancing Chemical Equations (cont.) ___N2O5(g)  ___N2(g) + ___O2(g)

Balancing Chemical Equations (cont.) ___Fe2Cl3  ___Fe(s) + ___Cl2(g)

Answer questions in the closure section of your bell ringer sheet.

A B C D Assessment Which of the following is NOT a chemical reaction? A. a piece of wood burning B. a car rusting C. an ice cube melting into water D. red litmus paper turning blue A B C D

Assessment What is the coefficient of bromine in the equation 2Al(s) + 3Br2(l) → 2AlBr3(s)? A. 1 B. 2 C. 3 D. 6 A B C D