Question

If 4kcal of heat is supplied to a gas and volume of gas changes from 5L to 55L against a constant external pressure of 2atm. Find change in internal energy

Answer 1

Given:

• Heat supplied =q = 4kCal
• Initial volume = 5L
• Final volume = 55L
• Exernal Pressure = 2atm

Need to find:

• Change in internal energy =?

Solution:

q= 4kCal

→ q = 4000 Cal

→ q = 4000 × 4.2 Jolues

→q = 16800Joules

Chnage in volume = Final volume - Initial Volume

→ Change in volume = 55L- 5L

→ Change in volume = 50L

Now,

Work done:

= (- Change in Volume × External Pressure)

= -2× 50 L.atm

= -100 L.atm

= -100× 101.3 Joules

= -10130 Joules

Change in Internal energy:

=Energy supplied - Energy released

= Heat supplied - Work done

= 16800- 10130 Joules

= 6670Joules (answer)