# Hard molar specific heat question?

1. Nov 4, 2012

### fantexihong

1. The problem statement, all variables and given/known data
At very low temperatures, the molar specific heat of many substances varies as the cube of the absolute temperature: C=k*(T^3/To^3),
which is sometimes called Debye's law. For rock salt, To= 281K and k= 1940 J/mol*K

Determine the heat needed to raise 2.40 mol of salt from 30.0K to 50.0K .

2. Relevant equations
I don't know if this equation applies to solid . Q=nC*ΔT

3. The attempt at a solution
I know ΔT is 20, it seems to me that the only unknown for this question is T.
I tried to plug in 30 OR 50 into T, but I got the wrong answer.

2. Nov 4, 2012

### Staff: Mentor

Q=nCΔT is OK, but to make things more difficult C is a function of temperature.

3. Nov 4, 2012

### fantexihong

Could you tell me how to get the C value for this question? I know C=k*(T^3/To^3) from the problem, it also gives me k and To value, but I don't know what is T value.

4. Nov 4, 2012

### Staff: Mentor

T is given in the problem and is not constant - it changes from 30 to 50 K. You need to integrate.

5. Nov 4, 2012

### fantexihong

It works!!!!!!I just need to integrate that C function, thank you!!!