# Homework Help: Small issue regarding the wording of a thermodynamics question

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1. Jan 3, 2018

### dregozo

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

The issue is the word 'increase' in c)iii), where I'm pretty sure the wording should have been 'decrease' or at least 'change', since both the work done and the heat removed have a negative value.
2. Relevant equations
dU = dQ + dW (1st law)

3. The attempt at a solution
My answer to c)iii) was -160J.

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2. Jan 3, 2018

### Bystander

"Increase" IS change; don't get your knickers in a knot.

3. Jan 3, 2018

### dregozo

Can't agree with you there, an answer of -160J can't possibly suit the description of an INCREASE in internal energy!

4. Jan 3, 2018

### Staff: Mentor

Something seems very wrong with this problem statement. If the initial and final states of the system are thermodynamic equilibrium states for an ideal gas, then we must have that $$\Delta (PV)=nR\Delta T$$ and
$$\Delta U=nC_v\Delta T$$Combining these two equations gives:$$\Delta U=\frac{C_v}{R}\Delta (PV)$$For a monoatomic ideal gas the ratio of the heat capacity to the gas constant is 1.5, and for a diatomic gas, it is 2.5. From the data given in the table, $$\Delta (PV)=-5\ J$$This doesn't seem compatible with the change of -160 J calculated from the work and the heat removed. Thoughts?