Chemical Change

• Reactants Products

• What happens to bonds in a chemical reaction?

• Broken, form new bonds

Some examples:

• Word equations

• Iron + Oxygen iron (III) oxide

• (word equation for the rusting of iron)

• Hydrogen peroxide water + oxygen

• (what happens when you pour this on an open cut? Bubbles of oxygen gas rapidly appear)

• Methane + oxygen carbon dioxide + water

• (major component of natural gas)

Chemical Equations

• Fe(s) + O2(g) Fe2O3(s)

• (rusting of iron)

• Symbols are used to represent states

Chemical Equations

• H2O2(aq) MnO2 H2O(l) + O2(g)

• Catalyst: a substance that speeds up the rate of a reaction but that is not used up in the reaction. It is neither a reactant nor a product. It is written above the arrow in an equation because it is not part of the reaction.

Symbols used in chemical equations (see Table)

Review:• Write a skeleton outline for the following

chemical reaction (include appropriate symbols):

• -solid sodium hydrogen carbonate reacts with hydrochloric acid to produce the aqueous sodium chloride, water, and carbon dioxide gas.

• NaHCO3(s) + HCl(aq) NaCl(aq) + H2O(l) +CO2(g)

Review:

• sulfur burns in oxygen to form sulfur dioxide

• S(s) + O2(g) SO2(g)

Balancing Chemical Equations

• Use an example of building a bicycle• 4 components: frames, wheels, handlebars, and

pedals• Frame + wheel + handlebar + pedal bicycle

(reactants) (product)• (why is this word equation inadequate?)

• F + W + H + P FW2HP2

• (this is called an unbalanced equation, in order to balance, the amount of reactants must equal the amount of products)

Balancing Chemical Equations

• coefficient: a small whole number that appears in front of a formula in a balanced chemical equation

• F + 2W + H + 2P FW2HP2

• Balancing a chemical equation is necessary so that it obeys the law of conservation of mass.

• balanced equation: each side of the equation has the same number of atoms of each element

Let’s try a few:

• H2(g) + O2(g) H2O(l)

• how would you balance this equation?

“Rules for Balancing Equations”• count the number of each atom: hydrogen

is balanced but oxygen is not

• put a coefficient of 2 in front of H2O, the oxygen is balanced but there are twice as many hydrogen atoms in the product as there are in the reactants

• to correct this, put a coefficient of 2 in front of H2

• 2H2(g) + O2(g) 2H2O(l)

Review: • Balance the following equations:

• AgNO3 + H2S Ag2S + HNO3

• 2AgNO3 + H2S Ag2S + 2HNO3

• MnO2 + HCl MnCl2 + H2O +Cl2• MnO2 + 4HCl MnCl2 + 2H2O + Cl2

• Demo: Copper(II) chloride with aluminum

• Activity: “Balancing Chemical Equations”