Question

A cube 22 cm on each side contains 2.5 g of helium at 20∘C. 1100 J of heat energy are transferred to this gas.

a) What is the final pressure if the process is at constant volume?

b) What is the final volume if the process is at constant pressure?

Answer 1

Each side of the cube is 22 cm=0.22 m. So volume of the cube is

Molecular weight of helium is 4 gm/mole

So, number of moles in 2.5 gm of helium is

For a gas at pressure P, occupying volume V at temperature T, ideal gas law states that

R is the universal gas consatnt

Putting the values,

Now 1100 J of heat is added.

So, corresponding increase in temperature at constant volume assuming specific heat at constant temperature to be 3.12J/gm degC

So, final temperature is

So, using Charle's law

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Specific heat at constant pressure is 5.19 J/gm deg C

So, rise in temperature is

So, final temperature is

Using volume law we have