Chemistry only- higher tier
The table below gives the formula and mass of 1 mole of a number of gases.
|gas||molecular formula||Ar or Ar||mass of 1 mole/g||volume gas will occupy at RTP/dm3|
Remember gases are mostly empty space with large gaps between the particles. The volume that
a gas occupies depends on its temperature and pressure. If you heat a gas up it will expand
and take up more space, and if you cool it then its volume will decrease. Squashing a gas or
putting it under pressure will also decrease its volume while reducing the pressure on a gas
it cause it to expand. So when you talk about the volume a gas occupies you should really state
the temperature and pressure as well.
In gcse chemistry we are mostly dealing with gases at room temperature and pressure (RTP), that is 200C or 293K and 1 atmosphere pressure. According to Avogadro's theorem 1 mole of any gas will occupy the same volume at any given pressure and temperature. This means for example that 2g of hydrogen will occupy the same volume as 32g of oxygen or 44g of carbon dioxide or 58g of butane or 4g of helium. At 200C and 1 atmosphere pressure 1 mole of any gas will occupy 24dm3 or 24 litres. This is called the molar volume of a gas.
Example. Calcium carbonate (CaCO3) decomposes when heated according to the equation below: