# How do I find the volume of a gas when the pressure and temperature changes, given the original volume? [closed]

I am a sophomore in high school, just started honors chemistry this year, and I'm having trouble figuring out what formula to use for this question, and how exactly to do so:

If a gas has an original volume of 6 L, an original temperature of 298.15 K, and an original pressure of 1 atm, what would the volume be at a temperature of 288.15 K and a pressure of .92 atm?

So far I thought that it would probably be best to use the formula, pV=nRT , but I have not been able to figure out what exactly R is. I know that it is the constant, but what is the value and/or how is it calculated? I have also been asked to use this formula in other questions, and I don't quite understand the value of R. If someone could help work me through this, that would be wonderful.

$$R$$ is the universal gas constant, the value of which you can find e.g. here. For this problem, you don't need to know the value, though.

$$p V = n R T \mathrm{\ \ \ or\ \ \ \ } R = \frac{p V}{n T}$$

is true for any ideal gas, and a pretty good approximation for most gases at room temperature or higher and atmospheric pressure or lower. So for two different samples 1 and 2 that behave like ideal gases, you can write:

$$\frac{p_1 V_1}{n_1 T_1} = \frac{p_2 V_2}{n_2 T_2}$$

In your case, $$n_1 = n_2$$. You can solve for $$V_2$$ and plug in the numbers to get the answer.

• Oh, okay! Thank you so much, I wasn't even aware I was using the incorrect formula. Appreciate the help! Commented Oct 15, 2021 at 16:33
• Just to be clear - the formula is not incorrect, it is just not in a mouth-sized portion for consumption yet. @GraciousBean
– Karsten
Commented Oct 15, 2021 at 17:12