chemistry 1.3

relative formula mass

explanation:

Mass changes when a reactant or product is a gas

Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas and its mass has not been taken into account. For example: when a metal reacts with oxygen the mass of the oxide produced is greater than the mass of the metal or in thermal decompositions of metal carbonates carbon dioxide is produced and escapes into the atmosphere leaving the metal oxide as the only solid product.

moles

Chemical amounts are measured in moles (mol). The mass of one mole of a substance (in grams) is equal to its relative formula mass. One mole of any substance contains the same number of particles (atoms, molecules, or ions). This number is called the Avogadro constant, which is 6.02 × 10²³ particles per mole.

Amounts of substances in equations

The masses of reactants and products can be calculated from balanced symbol equations. Chemical equations can be interpreted in terms of moles. For example: Mg+2HCI→MgCI2+H2 shows that one mole of magnesium reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride and one mole of hydrogen gas

Using moles to balance equations

The balancing numbers in a symbol equation can be calculated from the masses of reactants and products by converting the masses in grams to amounts in moles and converting the numbers of moles to simple whole number ratios.

Limiting reactants

In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used. The reactant that is completely used up is called the limiting reactant because it limits the amount of products.

Concentration of solutions

conc. = mass/volume

Percentage yield

formula:

atom economy

formula :

Using concentrations of solutions in mol/dm 3

The concentration of a solution can be measured in mol/dm3 . The amount in moles of solute or the mass in grams of solute in a given volume of solution can be calculated from its concentration in mol/dm3 . If the volumes of two solutions that react completely are known and the concentration of one solution is known, the concentration of the other solution can be calculated.

Use of amount of substance in relation to volumes of gases

Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure. The volume of one mole of any gas at room temperature and pressure (20o C and 1 atmosphere pressure) is 24 dm3 . The volumes of gaseous reactants and products can be calculated from the balanced equation for the reaction.