Closed container vs Open container for calorimetry

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In the reaction between magnesium and hydrochloric acid (Mg + HCl --> MgCl2 + H2), conducting the experiment in a closed calorimeter leads to an increase in pressure due to the accumulation of hydrogen gas (H2). The heat capacity of H2 is noted to be 14.31 kJ/(kg K) at 300K, which is significantly higher than that of air (1.00 kJ/(kg K)). This implies that in a closed system, the presence of H2 will absorb more heat, resulting in a smaller temperature increase of the liquid compared to an open calorimeter where H2 can escape. Therefore, the measured temperature change in the closed calorimeter is expected to be less than the 12 degrees Celsius observed in the open setup, as the heat capacity of H2 moderates the temperature rise. The reaction occurs solely in the liquid phase, with no air participating in the reaction.
Matthew Hoffman
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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?
 
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Does the H2 have a non-zero heat capacity?
 
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?
 
Matthew Hoffman said:
Am I headed in the right direction here?
... and?
 
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?
 
Matthew Hoffman said:
H2 does have a nonzero heat capacity.
Period, no need to compare it to air. Do you have any air reacting?
 
No, the reaction is only taking place in the liquid
 

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