# Thermodynamics entropy problem

1. Sep 21, 2009

### dancergirlie

1. The problem statement, all variables and given/known data
Find (a) the energy absorbed as heat and (b) the change in entropy of a 2.00 kg block of copper whose
temperature is increased reversibly from 25°C to 100°C. The specific heat of copper is 386 J/kg K .

2. Relevant equations

dS=dQ/T
dS=nRln(final volume/initial volume) **for an ideal gas**

3. The attempt at a solution\

Well I got the first part. The energy is just
dQ=cmdT
which is (386)(2)(75K)= 57900J

however, when i got to the second part, I didn't know what to do since the copper isn't an ideal gas, and it has a non-constant temperature so I can't use the first equation. Any help would be appreciated!!!

2. Sep 21, 2009

### dancergirlie

Entropy Thermodynamics problem

1. The problem statement, all variables and given/known data

Find (a) the energy absorbed as heat and (b) the change in entropy of a 2.00 kg block of copper whose
temperature is increased reversibly from 25°C to 100°C. The specific heat of copper is 386 J/kg K .

2. Relevant equations

dS=dQ/T
dS=nr ln(vf/vi) **for an ideal gas**

3. The attempt at a solution

The first part was relatively easy. I just used the equation:
dQ=cmdT
so, dQ=(386)(2)(75)=57900 J

But for the 2nd part, I dont know what to do because copper is not an ideal gas, ruling out the 2nd equation, and the temperature is not constant, meaning I cannot use the first equation. Any help would be great!!!

3. Sep 21, 2009

### Gear300

Re: Entropy Thermodynamics problem

dS = dQ/T
dQ = cmdT
dS = cmdT/T
Integrate both sides to get delta(S) = cm*ln(Tf/Ti); be sure to use Kelvin.
Its been a while since I've done thermodynamics, so I might be wrong...though I only applied a bit of mathematical procedure, so it seems as though it would be fine.

4. Sep 21, 2009

### dancergirlie

Re: Entropy Thermodynamics problem

sounds right to me.... thanks for the help!