Calorimetry

Question 1

what is calorimetry?

Answer 1

an experimental method used to measure an enthalpy change

Question 2

what happens in an exothermic calorimetry reaction?

Answer 2

1. the reaction releases heat energy
2. that heat energy is absorbed by the nearby water
3. the temperature of the water increases

Question 3

what are the two formulas to convert measurements into ΔH?

Answer 3

Q = mcΔH
and
ΔH = -Q/moles

Question 4

what is the simplest type of calorimetry?

Answer 4

involves combusting a fuel to heat up the water

Question 5

method to measure the ΔH for the combustion of liquid fuel

Answer 5

1. weigh out 50g of water and place in a can above the burner
2. measure the initial mass of the burner and the initial temperature of the water
3. ignite the burner, stir water for 30 seconds, then extinguish the burner
4. measure the final mass of the burner and the final (maximum) of the water

Question 6

what are two significant sources of error in a calorimetry experiment?

Answer 6

heat loss - most of the heat energy dissipates into the air instead of the water

incomplete combustion - this releases less heat energy than expected

Question 7

what happens if the reaction you are measuring results in being dissolved in some water?

Answer 7

the reaction still releases heat energy and the water still absorbs it - but it just happens that the reaction and the water are in the same place

Question 8

in solution calorimetry what are the potential sources of error in the experiment?

Answer 8

• as for combustion calorimetry, heat loss and incomplete reaction are potential sources of error
• as well as that, the water being heated is no longer pure water as it has things dissolved in it
• this means that the specific heat capacity is no longer exactly 4.2J/g

Question 9

what happens in a calorimetry experiment for endothermic reactions in a solution?

Answer 9

• the reaction absorbs heat energy from the water, so the water cools down
• this results in a negative temperature change for the water
• the minus sign gets passed through the equations and comes out at the end as a plus, because a minus x minus = plus
• this is good because reactions that absorb heat energy are endothermic and endothermic reactions have positive enthalpy changes (ΔH)