# Homework Help: Specific heat capacity of gases

1. Apr 23, 2015

### lavankohsa

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

Figure shows two rigid vessels A and B, each of volume 200 cm3 containing an ideal gas (Cv = 12.5 J/mol-K). The vessels are connected to a manometer tube
containing mercury. The pressure in both the vessels is 75 cm of mercury and the temperature is 300 . (b) 5.0 J
of heat is supplied to the gas in the vessel A and 10 J to the gas in the vessel B. Assuming no appreciable transfer of heat from A to B calculate the difference in the heights of mercury in the two sides of the manometer

2. Relevant equations

ΔQ=ΔW+ΔU

3. The attempt at a solution

I know that when we give heat to both vessel, the pressure will increase. So the mercury column will also move and there will be a difference in the height in two arms . But my book says when we give heat to vessl there of gas in both vessel will be same. So according to my book ΔW=0 for both vessel. But since mercury will move, one gas should expand and other should compress. Please help me .

2. Apr 23, 2015

### Staff: Mentor

They are assuming that the volume available for expansion and contraction of the gases within the manometer tube is negligible.

Chet

3. Apr 23, 2015

### lavankohsa

OK thanks . But they should mention it .

4. Apr 23, 2015

### Staff: Mentor

Yes, they should, since the figure seems to suggest that there is volume available for gas expansion and contraction in the manometer tube. But it obviously is not drawn to scale.

Chet