energetics exam qs

Question 1

The student follows this method:
* measure out 50 cm 3
of 1.00 mol dm–3 aqueous hydrochloric acid using a measuring
cylinder and pour the acid into a 100 cm3
glass beaker
* weigh out 2.50 g of solid calcium carbonate on a watch glass and tip the solid into the
acid
* stir the mixture with a thermometer
* record the maximum temperature reached.
The student uses the data to determine a value for the enthalpy change

Answer 1

1a. Use a burette/pipette (instead of a measuring cylinder)
1b. Use a polystyrene cup (instead of a beaker) / insulate beaker
1c. Reweigh the watchglass after adding the solid 1d: Use powdered solid
Stage 2: Temperature Measurements
2a. Measure and record the initial temperature of the solution for a few minutes before
addition
2b. Measure and record the temperature after the addition at regular intervals (eg each
minute) for 8+ minutes/until a trend is observed
Stage 3: Temperature Determination
3a. Plot a graph of temperature against time
3b. Extrapolate to the point of addition
3c. Determine ΔT at the point of addition

Question 2

State why the heat change calculated from the bomb calorimeter experiment is not an
enthalpy change.

Answer 2

pressure not constant in bomb calorimeter