partial pressure is the pressure exerted by an individual gas within a mixture. So think of it as the gas is individual pressure, we're going to say in a container of un reacting, gas is total pressure of the container is the sum of partial pressures of each gas. Now this is known as the law of partial pressures. So basically the total pressure inside of a container comes from adding up all the pressures of each individual gas. So total pressure would equal the pressure of gas one plus gas two plus gas three and so on. If there are additional gas, is so just remember, the total pressure that container is experiencing is contributed by each of the individual gasses within it.