RP2 - Measuring enthalpy change Flashcards

1
Q
A

One type of experiment is one in which substances are mixed in an insulated container and the temperature rise measured.

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2
Q

This could be a solid dissolving or reacting in a solution or it could be two solutions reacting together

A
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3
Q
A

General method
 washes the equipment (cup and pipettes etc) with the solutions to be used
 dry the cup after washing
 put polystyrene cup in a beaker for insulation and support
 Measure out desired volumes of solutions with volumetric pipettes and transfer to
insulated cup
 clamp thermometer into place making sure the thermometer bulb is immersed in solution  measure the initial temperatures of the solution or both solutions if 2 are used. Do this
every minute for 2-3 minutes
 At minute 3 transfer second reagent to cup. If a solid reagent is used then add the
solution to the cup first and then add the solid weighed out on a balance.
 If using a solid reagent then use ‘before and after’ weighing method
 stirs mixture (ensures that all of the solution is at the same temperature)  Record temperature every minute after addition for several minutes

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4
Q
A

If the reaction is slow then the exact temperature rise can be difficult to obtain as cooling occurs simultaneously with the reaction.

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5
Q
A

To counteract this we take readings at regular time intervals and extrapolate the temperature curve/line back to the time the reactants were added together.

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6
Q
A

We also take the temperature of the reactants for a few minutes before they are added together to get a better average temperature. If the two reactants are solutions then the temperature of both solutions need to be measured before addition and an average temperature is used.

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7
Q

errors in method

A

energy transfer from surroundings (usually loss)
* approximation in specific heat capacity of solution. The method assumes all solutions have the heat capacity of water.
* neglecting the specific heat capacity of the calorimeter- we ignore any energy absorbed by the apparatus.
* reaction or dissolving may be incomplete or slow.
* density of solution is taken to be the same as water.

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8
Q
A
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