How does one calculate the mass of gases in reactions?

One calculates the mass of gases in reactions using the ideal gas law and molar mass of the gas.

The ideal gas law is a fundamental principle in chemistry that states that the pressure of a gas times its volume is directly proportional to the number of moles of the gas and the temperature. This is often expressed as PV=nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature.

To calculate the mass of a gas in a reaction, you first need to know the volume of the gas at a known temperature and pressure. You can then use the ideal gas law to calculate the number of moles of the gas. Once you have the number of moles, you can then calculate the mass of the gas by multiplying the number of moles by the molar mass of the gas. The molar mass of a gas is the mass of one mole of the gas, and it can be found on the periodic table for each element.

For example, if you have a reaction that produces 22.4 litres of oxygen gas at standard temperature and pressure (0 degrees Celsius and 1 atmosphere), you can use the ideal gas law to calculate that this is equivalent to one mole of oxygen gas. The molar mass of oxygen is 16 g/mol, but because oxygen gas is O2, you need to multiply this by 2, giving a molar mass of 32 g/mol. Therefore, the mass of the oxygen gas produced in the reaction is 32 g.

Remember, this method assumes that the gas behaves ideally, which is a good approximation under many conditions, but not all. Real gases can deviate from ideal behaviour under extreme temperatures or pressures.