2) Measurement Of Enthalpy Change

Question 1

What main equation do we use for this experiment?

Answer 1

Q= mc(temp change)

Question 2

Describe the ‘calorimetric’ method.

Answer 2

1) wash and dry equipment
2) put polystyrene cup in a glass beaker for insulation and support
3) measure out desired volumes of solutions with volumetric pipettes and transfer into polystyrene cup
4) clamp thermometer into place making sure the thermometer bulb in immersed in solution
5) measure the initial temperatures of the solution, then repeat every minute for 3-4 minutes
6) at minute 4 transfer second reagent to cup.
7) stir mixture to ensure all the solution is at the same temperature and record temp every minute for several minutes

Question 3

Why do we record the temperatures of the reactants a few minutes before adding 2nd reagent?

Answer 3

-get a better average temp

Question 4

What should you remember to do when drawing these graphs?

Answer 4

• extrapolate the lines

- include temp change

Question 5

What are the errors to this method?

Answer 5

• energy transfer from surroundings (usually loss)
• assumes that all solutions have the same heat capacity
• neglecting the specific heat capacity of the calorimeter- ignore any energy absorbed by the apparatus
• reaction or dissolving may be incomplete
• density of solution is taken to be the same as water

Question 6

What is the general method in calculating the enthalpy change of a reaction?

Answer 6

1) use Q= mc(tempchange)
2) work out moles of reactants used
3) divide Q by the number of moles of reagent not in excess
4) add units