Measurement of an Enthalpy Change [RPA 2] Flashcards
1
Q
What is calorimetry?
A
Technique used to measure enthalpy change of a chemical reaction
2
Q
What is the equation to calculate enthalpy change?
A
3
Q
Enthalpy changes for reactions in solution METHOD and ASSUMPTIONS: Displacement reaction between zinc and copper sulfate solution
A
Assumptions :
- Specific heat capacity of solution is the same as water
- Density of solution is the same as water
- Specific heat capacity of container is ignored
- Reaction is complete
- Negligible heat loss
4
Q
Why extrapolate the cooling gradient of the graph?
A
- Reactions are not instantaneous
- Delay before maximum temperature is reached
- During this delay, substances may be losing heat to surroundings
- So true maximum temperature is never reached
- So extrapolate with a line of best fit for cooling section up to the point in time where the reactant was added
- To find the theoretical maximum temperature
5
Q
How do enthalpy of combustion experiments work?
A
- Heat released by combustion
- Increases heat content of the water
- Calorimeter used to measure temperature changes to water
6
Q
Calculating Enthalpy of Combustion of a reactant METHOD :
A
- Fill copper can with 100cm^3 of water
- Record initial temp with thermometer
- Measure mass of empty spirit burner (weighing scale) and measure it again after adding fuel. Record masses
- Light the wick, stir water for set time until the fuel is completely burnt
- Record final temp of water
- Measure mass of burner and any remaining fuel to find the mass of the fuel burnt
7
Q
What are some issues with these practicals? How can they be prevented?
A
- Some heat is lost to the surroundings
- Some heat energy can be absorbed by the calorimeter
- Incomplete combustion can occur (releases less energy)
. - Copper calorimeter should not be placed too far above flame
- Lid onthe calorimeter
- Shielding can reduce draughts
