For many purposes we can treat ammonia NH3 as an ideal gas at temperatures above its boiling point of -33 degrees celsius.

Question

Suppose the temperature of a sample of ammonia gas is raised from -14.0 °C to 21.0 °C, and at the same time the pressure is changed. If the initial pressure was 6.5 atm and the volume increased by 50.0% , what is the final pressure? Round answer to the correct number of significant figures.

Answer 1

This is a classic combined gas law problem. If the number of moles is kept constant, an ideal gas follows the relationship

P₁V₁/T₁=P₂V₂/T₂

The only thing we have to be careful of is that the temperature must be absolute (in kelvins) for all of the gas laws. The other thing about this problem, in particular, is that they didn't actually give us volumes. But they told us it increases 50%, so we can say that V₂=1.5V₁. This way, V₁ will cancel on both sides of the equation.

Solving for P₂ = P₁V₁T₂/T₁V₂

Again, substituting 1.5V₁ for V₂, we get P₂ = P₁V₁T₂/T₁1.5V₁ = P₁T₂/1.5T₁