Solutions and answers for classroom tasks and homework

Task 2.

Helium is a monatomic gas, therefore its internal

energy is determined by the formula . At a temperature

Т = 127+273= 400 К this energy is equal U=3/2*8,31*400=5000 J

1.

What is the internal energy of 10 moles of argon at 27⁰С ?

U=3/2* ʋRT
T=273+27=300 K
Consequently U=3/2 *10*8.31*300=37395 J

2.

Find the internal energy U mass m=20 g oxygen at temperature t = 10 °С.

3.

Find the internal energy U diatomic gas, located in a vessel V = 2 L under pressure

р = 150 kPa.

Homework solutions and answers

1)      Nitrogen is diatomic gas (N₂).

U = ·nRT

n =         (M(N₂) = 28·10^-3 kg/mole)

U = ··8.314 J/(mole·K)·283 K

U ≈ 4.2 kJ

2)      Helium is monatomic gas (He).

U = ·nRT

PV = nRT

U = ·PV

U = ·100·10³ Pa·60 m³

U = 9 MJ

3)      n = const   (m = const)

 =

ΔT = T₂ – T₁

ΔU = ·nRΔT

P₂ = 3P₁

V₂ =

 =  => T₂ = 1.5T₁

ΔU = ·nR0.5·T₁

U₁ = ·nRT₁

U₂ = ·nR·1.5T₁

Internal energy will be increased by half of initial

OR

Internal energy will be increased by 1.5 times