RP2 - Measuring Enthalpy Change

Question 1

What is Hess’s Law?

Answer 1

1. The overall enthalpy change of a reaction is always the same regardless of the reaction pathway taken

Question 2

How can you reduce uncertainty in a mass measurement?

Answer 2

1. Use a balance with a greater resolution
2. Use a larger mass

Question 3

How do you calculate percentage uncertainty?

Answer 3

100 x absolute uncertainty / calculate value

Question 4

What equation is used to calculate enthalpy change?

Answer 4

1. q=mc𝚫T

Question 5

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

Answer 5

1. Heat loss to apparatus / surroundings
2. Incomplete combustion
3. Non-standard conditions
4. Evaporation of alcohol/water

Question 6

How do you prevent heat loss to surroundings / apparatus?

Answer 6

1. Insulate the beaker by placing it in a polystyrene cup with a lid
2. Avoid large temperature differences between surroundings and a calorimeter
3. Use a bomb calorimeter