Question

A gas system absorbs 450 cal of heat and the work done by the system is 200 cal. Then the change in the internal energy of the system is ........... cal.
(A) 250
(B) 850
(C) 325
(D) zero

Answer 1

Answer:

(A) 250 cal

Explanation:

As per the question,

According to first law of thermodynamics  energy cannot be created and cannot be destroyed as well.In mathematical terms it is expressed as the change in internal energy which is related as:

ΔU = Q+W

Where ΔU = change in internal energy

            Q = heat absorb

             W = work

Now the given data of question is:

Q = heat absorb by the system = +450 cal

W = work done by the system = -200 cal

(As work done by the system is negative)

Substitute the value in ΔU = Q+W

⇒ΔU = 450+(-200)

⇒ΔU =250 cal.

Hence , the correct option is (A).

Answer 2

Answer:

change in internal energy (U) = +250 cal

Explanation:

●Heat absorbed (Q) = +450 cal

●Work done by the system (W) = +836.2 J

●Change in internal energy (U) in cal = (?)

●To convert Joule to Calorie,

÷4.19

hence,

$= \frac{836.2}{4.186}$

= 199.7 cal

=200 cal

●According to the Fiest law of Thermodynamic,

deltaQ = deltaU + deltaW

450 = deltaU + 200

deltaU = 450 - 200

deltaU = +250 cal

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