Agas is compressed from 600cm3 to 200cm3 at a constant pressure of 450kpa . at the same time, 100j of heat energy is transferred out of the gas. part awhat is the change in thermal energy of the gas during this process?

80J

Explanation:

According to the first principle of thermodynamics:  

"Energy is not created, nor destroyed, but it is conserved."  

Then this priciple (also called Law) relates the work and the transferred heat exchanged in a system through the internal energy , which is neither created nor destroyed, it is only transformed. So, in this especific case of the compressed gas:

 (1)

Where:

is the variation in the internal (thermal) energy of the system (the value we want to find)

is the heat transferred out of the gas (that is why it is negative)

is the work is done on the gas (as the gas is compressed, the work done on the gas must be considered positive )

On the other hand, the work done on the gas is given by:

 (2)

Where:

is the constant pressure of the gas

is the variation in volume of the gas

In this case the initial volume is and the final volume is .

This means:

 (3)

Substituting (3) in (2):

 (4)

 (5)

Substituting (5) in (1):

 (6)

Finally:

 This is the change in thermal energy in the compression process.