Week 3

Question 1

Rules of balancing chemical equations

Answer 1

1. write your unbalanced equation
2. change only coefficient, don’t touch subscripts
3. count number of atoms that appear on each side
4. begin with elements that appear only in one product and reactant
5. balance most metallic elements first
6. leave hydrogen and then oxygen until last
7. ensure coefficients are in lowest possible ratio

Question 2

What are chemical reactions?

Answer 2

Involve charge with atoms, molecules or ions rearranging to form new substances. In the process, chemical bonds are broken and new bonds are formed.

Question 3

Components of writing down a chemical reaction

Answer 3

• reactants
• state of material
• arrow (yields)
• process applied (above arrow)
• products

Question 4

Reactants

Answer 4

Substances that are changed in a chemical reaction

Question 5

Products (of a reaction)

Answer 5

Substances created as a result of a chemical reaction

Question 6

Steps to write a chemical equation

Answer 6

• identify starting materials
• indicate proportions (stoichiometry) in which they are present
• indicate any products formed

Question 7

Steps to doing calculations involving chemical reactions

Answer 7

• write a balanced equation for the reaction
• convert all masses to moles to allow direct comparison of species in chemical reaction
• compare stoichiometry in equation to the moles calculated and determine the limiting reagent
• determine products formed
• convert product moles back to mass to express final answer

Question 8

Why must we calculate yields?

Answer 8

Chemical reactions rarely go to completion and stoichiometric equations show the optimum case in the conversion of reactants to products (100%)

Question 9

% yield

Answer 9

% yield =the actual product yield/maximum possible yield x 100

Question 10

Alkali metals and water

Answer 10

Group 1 metals react with water to produce a basic solution (a hydroxide) and hydrogen. Violent and exothermic reaction.

Question 11

General alkali metal and water reactions

Answer 11

2M(s) + 2H20 —-> 2MOH(aq) + H2(g)

Question 12

Combustion of hydrocarbons

Answer 12

• hydrocarbons (compounds containing carbon and hydrogen) burn in excess oxygen to produce carbon dioxide and water

Question 13

Combustion of hydrocarbons general reaction

Answer 13

R + O2(g) —> CO2(g) + H2O(l)

Question 14

Acid base reactions

Answer 14

Acidic compounds will react with a base to produce a salt and a water
Acid + base —> salt + water

Question 15

Acid carbonate reactions

Answer 15

Acidic and hydrogen carbonate and carbonate salts combine to produce a salt, carbon dioxide and water

Question 16

General acid carbonate reactions

Answer 16

2HA + M2CO3 —> 2MA + CO2(g) + H2O(l)