Question

In a chemical reaction ,system absorbs 500 J of heat and does work. The change in internal energy is 250 J.The work done will be​

Answer 1

Given:

In a chemical reaction ,system absorbs 500 J of heat and does work. The change in internal energy is 250 J.

To find:

Work done ?

Calculation:

According to 1st Law of Thermodynamics :

$\rm\therefore \: \Delta Q = \Delta U + W$

Now , since heat is absorbed , the sign for ∆Q will be positive.

Now 2 cases arise :

If ∆U is positive:

$\rm\implies \: + 500= + 250+ W$

$\rm\implies \: W = 500 - 250$

$\rm\implies \: W = 250 \: joule$

So, work done is +250 Joule.

If ∆U is negative :

$\rm\implies \: + 500= - 250+ W$

$\rm\implies \: W = 500 + 250$

$\rm\implies \: W =750 \: joule$

So, work done is +750 Joule.