Question

A system does 200j of work and at the same time absorbs 150 j of heat. What is the change in internal energy?

Answer 1

ANSWER:50J                                                                                                        Explanation:

Internal energy =work done + heat                                                                                                           as the work is done by the system so it is negative                                                       -200+150=50

Answer 2

Given:

System does 200 J of work , and simultaneously absorbs 150 J of heat.

To find:

Change in Internal Energy of the system

Concept:

We shall apply 1st Law of Thermodynamics to solve this problem ;

1st Law of Thermodynamics states that the Internal Energy change of any system is equal to the total heat change plus the work done.

Mathematical represention of 1st Law of Thermodynamics:

[ Let ∆U be Internal Energy change , ∆Q be change in heat content and W be the work done/on the system ]

$\boxed{ \sf{\Delta U = \Delta Q + W}}$

• ∆Q is considered to be positive if heat is added to system and vice-versa.

• W is considered negative if it is done by the system itself and vice-versa.

Calculation:

$\therefore\sf{\Delta U = \Delta Q + W}$

$= > \sf{\Delta U = ( + 150) + (- 200)}$

$= > \sf{\Delta U = - 50 \:J }$

So the Internal Energy of the system decreases by 50 J.