Closed container vs Open container for calorimetry

[Matthew Hoffman]

So let's say I do the reaction Mg + HCl --> MgCl2 + H2 in an open calorimeter. I measure a certain temperature change in the calorimeter, let's say an increase of 12 degrees C. Keeping all other variables the same, if I perform this experiment in a closed calorimeter, what will happen to the measured temperature? I know the pressure of the gas will increase because of the compressed H2, but will this have any affect on the temperature of the liquid below it?

 

[Bystander]

Does the H₂ have a non-zero heat capacity?

 

[Matthew Hoffman]

H2 does have a nonzero heat capacity. At 300K, it is 14.31 (kJ/(kg K)). Compared to air, which has a value of 1.00. And in a closed container, the mixture of gases would contain much more H2 than in an open container where it would escape. Am I headed in the right direction here?

 

[Bystander]

Am I headed in the right direction here?

... and?

 

[Matthew Hoffman]

And... since H2 has a greater heat capacity its temperature will not increase as much as plain air, so that means the measured temperature in the calorimeter would be less?

 

[Bystander]

H2 does have a nonzero heat capacity.

Period, no need to compare it to air. Do you have any air reacting?

 

[Matthew Hoffman]

No, the reaction is only taking place in the liquid