Photo AI
A student does an experiment to determine a value for the enthalpy of combustion of heptane - AQA - A-Level Chemistry - Question 3 - 2021 - Paper 2
Question 3
A student does an experiment to determine a value for the enthalpy of combustion of heptane. Figure 2 shows some of the apparatus used. Design a table to record all... show full transcript
Worked Solution & Example Answer:A student does an experiment to determine a value for the enthalpy of combustion of heptane - AQA - A-Level Chemistry - Question 3 - 2021 - Paper 2
Step 1
Design a table to record all the readings necessary to determine an experimental value for the enthalpy of combustion for heptane in this experiment.
Answer
| Parameter | Unit (if applicable) |
|---|---|
| Initial Temperature | °C |
| Final Temperature | °C |
| Mass of Calorimeter | g |
| Mass of Heptane | g |
| Time taken for reaction | minutes |
Step 2
Suggest two disadvantages of using a glass beaker on a tripod and gauze.
Answer
-
Glass is a poorer conductor than copper, which may result in inefficient heat transfer during the combustion process.
-
Using a tripod and gauze would create a height above the flame, causing heat loss to the surroundings, leading to less accurate results.
Step 3
Suggest two reasons why the value of enthalpy of combustion from this experiment is less exothermic than a data book value.
Answer
-
Heat loss to the surroundings or the copper/calorimeter during the experiment may result in lower measured heat output.
-
Incomplete combustion of heptane could lead to reduced energy release compared to the theoretical value.
Step 4