First slide

First law of thermodynamics

Question

Find the external work done by the system in kcal, when 20 kcal of heat is supplied to the system the increase in the internal energy is 8400 J) J = 4200J/kcal)

Easy

A

16 kcal
B

18 kcal
C

20 kcal
D

19 kcal

Solution

$\Delta Q = 20kcal;\Delta U = 8400J;\Delta W = ?$
$J = 4200J/kcal:\Delta U = \frac{{8400}}{{4200}} = 2kcal$
$\Delta Q = \Delta U + \Delta W$
$\Delta W = \Delta Q - \Delta U = 20 - 2 = 18kcal\$

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