required practical 2

Question 1

what is the aim of this practical?

Answer 1

to measure and calculate enthalpy changes of combustion for different alcohols

Question 2

what is the method for this practical?

Answer 2

1. measure out 100cm3 of water with a measuring cylinder and pour into a calorimeter (copper can)
2. measure the initial mass of the spirit burner containing the first alcohol with a mass balance
3. position the calorimeter directly above the spirit burner with a clamp and boss
4. measure the initial temperature of the water with a thermometer
5. remove the cap of the spirit burner and immediately light the wick - heat until the water temperature increases by 30 degrees
6. after replacing the cap on the spirit burner, immediately measure the new temperature of the water
7. measure the new mass of the spirit burner
8. calculate the temperature increase of the water and mass of fuel which was burnt
9. repeat for the other alcohols
10. calculate the enthalpy changes

Question 3

how do you calculate the enthalpy change of combustion for each alcohol?

Answer 3

first do q = mc ∆ T (all values in terms of water) to find the change in heat energy
then calculate how many moles of alcohol burnt using the value for mass that burnt
finally find the enthalpy change by doing ∆ H = q/ moles x 1000

Question 4

what is the mass of water used the same as?

Answer 4

the volume of water used

Question 5

what sources of error may cause your calculated enthalpy change to be lower than the actual standard values?

Answer 5

1. while the spirit burner is uncapped but not lit, fuel will evaporate (seems like more fuel burnt than actually did)
2. not all the heat energy released by the fuel is transferred to the water
3. the fuel doesn’t undergo complete combustion (less energy released in incomplete)
4. experiment not done under standard conditions