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# enthalpy change help

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1. I thought the answer for a) was faster rate of reaction ... the ms answer was less time for cooling - what has this got with the decreased surface area

and how does less time for cooling make it a more accurate enthalpy change value??
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2. I'll take a wild stab in the dark but this is what I think they mean by it.

Since you're measuring the temperature change of the solution, any heat loss to the surroundings will reduce the accuracy of the experiment.

Using finely powdered magnesium carbonate has a much higher surface area (for reaction) compared with a lump. it's therefore true that the rate of reaction will indeed be much faster (higher surface area means increased frequency of successful collisions)

Higher rate of reaction means the reaction occurs much more quickly, and so the temperature increase will be more sudden. This means that the time taken to complete the experiment will be much shorter, therefore meaning there is 'less time for cooling' i.e. the heat loss to the surroundings will be reduced simply because the same reaction is occurring, but over a much shorter period of time.

In essence: Faster rate of reaction => Less time for heat to be lost to surroundings => more accurate maximum temperature => more accurate enthalpy change value calculated
3. (Original post by Spectral)
I'll take a wild stab in the dark but this is what I think they mean by it.

Since you're measuring the temperature change of the solution, any heat loss to the surroundings will reduce the accuracy of the experiment.

Using finely powdered magnesium carbonate has a much higher surface area (for reaction) compared with a lump. it's therefore true that the rate of reaction will indeed be much faster (higher surface area means increased frequency of successful collisions)

Higher rate of reaction means the reaction occurs much more quickly, and so the temperature increase will be more sudden. This means that the time taken to complete the experiment will be much shorter, therefore meaning there is 'less time for cooling' i.e. the heat loss to the surroundings will be reduced simply because the same reaction is occurring, but over a much shorter period of time.

In essence: Faster rate of reaction => Less time for heat to be lost to surroundings => more accurate maximum temperature => more accurate enthalpy change value calculated
thanks SO much
4. (Original post by pondsteps)
I thought the answer for a) was faster rate of reaction ... the ms answer was less time for cooling - what has this got with the decreased surface area

and how does less time for cooling make it a more accurate enthalpy change value??
I have to say that's the answer I would have chosen as it seems more obvious.

However, higher surface area means more of the magnesium carbonate is in contact with its cooler surroundings, so there is less depth for the heat to be lost from. It does make sense, but really isn't an obvious answer!

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