Question

Find the change in internal energy of
the system which absorbs 2K.cal of
heat and at the same time it does
500 J of work (J=4.2 J/cal)
(A) 9000 J
(B) 8000 J
(C) 7900 J
(D) 7500 J​

Answer 1

Answer:

(C) 7900 J

Explanation :-

This question uses the formula of first law of thermodynamics which is :-

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

• Here,∆Q is heat change.∆U is change in internal energy.W is work done.

• In physics,work done by the gas is positive while work done on the gas is taken negative.(Opposite to Chemistry).

• The heat given to the system (absorbed) is taken as positive and the heat released is negative.

Calculations

Here, ∆Q = 2 KCal = 2000 Calorie. = 2000 × 4.2 J

∆Q = 8400 J (positive as it is absorbed)

W = 500 J ( Positive as done by the system)

Using, ∆Q = W + ∆U

=> 8400 = 500 + ∆U

=> ∆U = 8400 - 500 J

=> ∆U = 7900 J

Answer 2

Explanation:

ANSWER ✍️

C) 7900 J

Explanation :-

This question uses the formula of first law of thermodynamics which is :-

\boxed{\Delta Q \:=\: \Delta U \:+\:W}

ΔQ=ΔU+W

Here,∆Q is heat change.∆U is change in internal energy.W is work done.

In physics,work done by the gas is positive while work done on the gas is taken negative.(Opposite to Chemistry).

The heat given to the system (absorbed) is taken as positive and the heat released is negative.

Calculations

Here, ∆Q = 2 KCal = 2000 Calorie. = 2000 × 4.2 J

∆Q = 8400 J (positive as it is absorbed)

W = 500 J ( Positive as done by the system)

Using, ∆Q = W + ∆U

=> 8400 = 500 + ∆U

=> ∆U = 8400 - 500 J

=> ∆U = 7900 J

hope this helps you!!

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