Molecular Physics | Thermodynamics Answers

1kg of fluid is compressed reversibly according to a law pv=0.25. the final volume is1/4 of the initial volume. calculate the work done on the fluid and sketch the process on a p-v diagram

An automobile engine provides 568 Joules of work to push the pistons.
In this process the internal energy changes by -2778 Joules.

Calculate q for the engine. The represents the amount of heat that must be carried away by the cooling system.

when can a gas be describe as a vapour?

A .48kg piece of wood floats on water but is found to sink in alcohol (sg=.79). What is the sg of the wood?

On a P-V diagram starting from an initial state P0 V0 plot an adiabatic expansion to 2V0 an isothermal expansion to 2V0 and an isobaric expansion to 2V0.

a) Use this graph to determine in which process the least work is done by the system
b) If, instead, the substance was compressed to V0/2, in which process would the least work done ?
c) Plot the processes of parts (a) and (b) on P-T diagram starting from P0 T0. Indicate expansions and compressions and be careful to show relative positions at the endpoints of each process.

8. A rod 20 cm long, has both its ends maintained at 0*C at all times. At time t = 0 the
temperature distribution in the rod is

T (x,0) = { 50*C for 0<x<10cm
{0*C for 10cm<x<20cm

Obtain the temperature distribution u(x,t) in the rod if u(x,t) satisfies the diffusion
equation:

d^2 u(x,t) / dx^2 = 0.5 ( du(x,t)/dt )

17 It is NOT possible to completely convert
heat into internal energy
mechanical energy into heat
internal energy into mechanical energy
internal energy into heat

18 The second law of thermodynamics
is a statement of the law of conservation of energy
say that heat cannot be completely converted into mechanical energy
is the basis for the definition of temperature
is the basis for the definition of internal energy

15 The average kinetic energy of the molecules of an ideal gas in a close, rigid container is increased by a factor of 4. What happens to the pressure of the gas?
It remains constant
It increases by a factor 2
It increases by a factor of 4
It increases by a factor of 8

16 At what temperature will the root-mean-square speed of oxygen molecules have the value of 640 m/s? 1 kilomole of oxygen has a mass of 32kg.
252.5oC
332.3oC
272.2oC
373.2oC

13 A 0.5kg piece of metal (c = 600/kgK) at 300 degree celcius is dumped into a large pool of water at 20 degrees celcius. Assuming the change in temperature of water to be negligible, calculate the overall change in entropy for the system
85.5J/K
67.4J/K
122.3J/K
202.3J/K

14 Calculate how much heat is needed to be supplied to a gas at a pressure of
1.25×105Pa
, such that the pressure increases by 25 per cent at constant volume, and the internal energy by 120J.
240J
120J
320J
480J

9 The first law of thermodynamics may be written in he form
ΔU=ΔQ+ΔW
, where the symbols have their usual meaning. Which of the following is correct for the case of an isothermal expansion of an ideal gas?
ΔW>0
ΔW=0
ΔU=0
ΔU>0

10 Which statement about internal energy is correct
The internal energy of a system can be be increased without transfer of energy by heating
The internal energy depends only on its temperature
When the internal energy of a system is increased, its temperature always rises
When two system have the same internal energy, they must be at the same temperature