Closed container vs Open container for calorimetry

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Discussion Overview

The discussion revolves around the effects of using an open versus a closed calorimeter for the reaction between magnesium and hydrochloric acid, specifically focusing on the temperature change measured in the calorimeter. The scope includes theoretical considerations of heat capacity and gas behavior during the reaction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how the measured temperature in a closed calorimeter would compare to that in an open calorimeter, noting that the pressure of hydrogen gas will increase in the closed system.
  • Another participant inquires about the heat capacity of hydrogen gas, suggesting it may influence temperature measurements.
  • A participant confirms that hydrogen has a non-zero heat capacity and suggests that the closed container would retain more hydrogen gas than the open container, potentially affecting temperature change.
  • One participant speculates that because hydrogen has a greater heat capacity than air, the temperature increase in the calorimeter might be less in the closed system.
  • Another participant emphasizes the relevance of hydrogen's heat capacity without comparing it to air, questioning the presence of air in the reaction.
  • A participant clarifies that the reaction occurs only in the liquid phase, indicating that air is not involved in the reaction process.

Areas of Agreement / Disagreement

Participants express differing views on the implications of hydrogen's heat capacity and the effects of using a closed versus open calorimeter. There is no consensus on how these factors will definitively affect the measured temperature.

Contextual Notes

Participants have not fully resolved the implications of heat capacity differences and the behavior of gases in the calorimeter, leaving some assumptions and dependencies on definitions unaddressed.

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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