how many moles of gas?

Question

A gas with an initial temperature of 790 °C undergoes an isobaric process . Final temp = 81.3 C

A) How many moles of gas are there?

 

Hint:You must use Pascal for pressure and cubic meters for volume. The conversion to Pascal from atmospheres is easy: 1atm=101300Pa .

Answer 1

We need to use the Ideal Gas Law for this.

 

PV = nRT

 

Where

 

P is pressure

V is volume

n is the number of moles of gas

R is the universal gas constant

T is the temperature

 

Isobaric means that the pressure does not change. So let's put all the constants to one side of the equation. n and R are constants all the time, and P is constant for this problem. We see that...

 

V/T = nR/P

 

Where that group of stuff on the right is a constant. We conclude, then, that the ratio of V/T is some constant so any combination of V/T needs to be equal to any other ratio of V/T. As an equation, that looks like

 

V₁/T₁ = V₂/T₂

 

Now, it looks like you left out some information, because we clearly need one of these volumes to solve this. Once you have 1 volume, though, we can directly solve for the other volume. Then, once we have all the information, we can use the Ideal Gas Law to solve for the number of moles of gas, using wither set of data.