Chemical Reactions

Representing a Chemical Reaction:A chemical reaction is always represented in a

certain way : At the start of a reaction At the end of a reaction

we have we have Reactants Products

HCl (aq) + Ca(OH)2 (s) CaCl2 (aq) + 2 H2O (l)

The reactants and products can be in various states, and it is important to note if they are aqueous ,(aq), gas, (g), liquid, (l), or solid ,(s).

Law of Conservation of Matter:Balancing Chemical Reactions

Matter cannot be created nor destroyed. • The total mass of the reactants in a chemical

reaction must be equal to the total mass of the products formed.

• The coefficients in a chemical reaction must always be balanced in order to ensure that there are an equal number of each atom on both “sides” of the reaction.

Examples:• Place the correct coefficient in each blank

space in order to balance the following reactions:

__ MgF2 + __ K __ KF + __ Mg

__ H2 + __ O2 __ H2O

__ Al + ___ O2 ___Al2O3

** EST Molar Ratios & Stoichiometry

The coefficients in a chemical reaction are very important. They give us the molar ratio in which the substances react and form.

1HCl (aq) + 1Ca(OH)2 (s) 1CaCl2 (aq) + 2 H2O (l)

In the above example, the coefficients show that when 1 mole of HCl reacts with 1 mole of Ca(OH)2 there will always be 1 mole of CaCl2 and 2 moles of H2O formed.

We can use the molar ratios to determine the quantity (mass or moles) of reactants or products in a chemmical reaction.

Any calculation that uses the molar ratio is a stoichiometric calculation.

Example:2HCl (aq) + 1Ca(OH)2 (s) 1CaCl2 (aq) + 2 H2O (l)

a. Using the molar ratio, how many moles of H2O would form if 6 moles of HCl react with 3 moles of calcium hydroxide?

b.How many moles of calcium chloride are formed when 180 grams of water if formed?

1HCl (aq) + 1Ca(OH)2 (s) 1CaCl2 (aq) + 2 H2O (l)

m

M

n

Ex. What mass of oxygen is required to produce 4.4 grams of carbon dioxide, CO2?

C2H4 (g) + 3O2 (g) 2CO2 (g) + 2H2O (l)

m

M

n

4.4 g

44 g/mol

0.1 mol0.15 mol

32 g/mol

4.8 g