| What is the law for conservation of energy | total mass of reactants = total mass of products |
| What is the relative formula mass | The sum of the relative atomic masses of each atom in the formula |
| Why might mass be lost in a chemical reaction | If one of the reactants or products is a gas, it can escape |
| What happens when we burn wood | CO2 + H20 and other gases, these gases can escape and go into the atmosphere |
| What happens when metals corrode | The mass of the oxide produced will be larger as they recieve more oxygen atoms from the atmosphere |
| What happens in the reaction of zinc and hydrochloric acid | H2 is produced which can escape decreasing the mass |
| Uncertainty in chemical measurements | Every chemical measurement contains some uncertainty because for exam a digital thermometer measures to a precision of +/-0.1 leaving room for uncertainty |
| How do we reduce uncertainty in chemical measurements | Repeat the measurements and find a average |
| Why must a chemical equation be balanced | To make sure that there are the same number of atoms of each element before and after a reaction |
| What does the molecular formula show us | Actual amount of atoms which make up a molecule |
| What does the empirical formula show us | The simplest ratio of atoms which make up a molecule |
