Use the following key to draw molecules like we did yesterday to show 2 molecules of C2H6 reacting with oxygen molecules to form carbon dioxide and water. C = H = O = You will need to figure out how many oxygen molecules are needed – use all of the carbon and hydrogen first.

Tally # of symbols on each side of the arrow. Turn into an equation.

Chapter 8 Chemical Reactions 8-1 Describing Chemical Change

Word equations are useful to show reactants and products Recall “ “ equals yields, gives or produces May be written in sentence form or as an equation.

Chemical Equations More effective and easier to use than word equations. Formulas are used instead of words Fe + O2 Fe2O3 Skeleton Equation – does not show relative amount of reactants and products

Other Information in the equation State of matter: (s) = solid (l) = liquid (g) = gas (aq) = aqueous – dissolved in water Catalyst – substance that speeds up rate of reaction

Balancing Chemical Equations Skeleton equations show what is involved in the reaction but not relative amounts. To obey the law of conservation of mass, the number of atoms of each type must be the same on both sides of the equation. This is accomplished by adding coefficients and never changing the subscripts.

Rules for Balancing Equations Write the correct formula for each reactant and product. Working with one atom, adjust coefficients to balance that atom. If a polyatomic the same on both sides, balance as a unit. Do H’s and O’s last if possible. Reduce coefficients if possible

Hydrogen and oxygen react to form water Hydrogen and oxygen react to form water. Write a equation for this reaction. Aluminum reacts with oxygen in the air to form a thin protective coat of aluminum oxide.