Question

Four moles of a perfect gas heated to increase its temperature by 2°C absorbes heat of 40 cal at
constant volume. If the same gas is heated at constant pressure the amount of heat supplied is,
(R - 2 cal/mol K)
1) 28 cal
2/56 cal
3) 84 cal
4) 94 cal
​

Answer 1

Heat supplied at constant volume

Q

v

=

n

C

v

△

T

Qv=nCv△T

40

=

4

×

C

v

×

2

40=4×Cv×2

C

v

=

5

Cv=5 cal/mol.K

C

p

=

C

v

+

R

=

5

+

2

=

7

c

a

l

/

m

o

l

.

k

Cp=Cv+R=5+2=7cal/mol.k

⇒

⇒ Heat supplied at constant pressure

Q

p

=

n

C

p

△

T

=

4

×

7

×

2

Qp=nCp△T=4×7×2

Q

p

=

56

c

a

l

Qp=56cal