RP2: Measuring Enthalpy Change

Question 1

What is Hess’ Law?

Answer 1

The enthalpy change for a reaction is independent of the route taken.

Question 2

How can you reduce the uncertainty in the mass measurement?

Answer 2

Use a balance with a greater resolution and use a larger mass.

Question 3

What is percentage uncertainty and how do you calculate it?

Answer 3

% uncertainty = (actual/theoretical) x 100

Question 4

How do you calculate enthalpy change experimentally?

Answer 4

q = MCT

Question 5

Why may an experimental value for enthalpy change be different to the theoretical value?

Answer 5

• Heat loss to surroundings
• Incomplete combustion
• Non-standard conditions
• Evaporation of alcohol or water

Question 6

How do you prevent heat loss to surroundings?

Answer 6

• Insulate the beaker
• Avoid large temperature differences between surroundings
• Use a bomb calorimeter

Question 7

Other than preventing heat loss, how can the accuracy of this experiment be improved?

Answer 7

• Read the thermometer at eye level
• Stir the solution so the temperature is evenly distributed
• Use a digital thermometer for more accurate readings
• Use greater conc and masses = greater temp change

Question 8

What is accuracy?

Answer 8

The more accurate the data, the closer is it to the actual value.