Energetics (Enthalpy) - exam practice
Energetics (Enthalpy)
Question 1 of 3
A student is investigating the energy change when a salt dissolves in water to form a solution.
The student's method is given below:
- Add 75 cm3 distilled water to a polystyrene cup.
- Measure the initial temperature of the water.
- Add a known mass of copper sulfate to the water and stir with the thermometer until it has dissolved.
- Observe the thermometer and record the maximum temperature reached by the solution.
Explain why the student is using a polystyrene cup instead of pouring the water into a glass beaker.
The diagram below shows the thermometer before the copper sulfate is added and the maximum temperature reached.
Calculate the change in temperature of the copper sulfate solution.
Calculate the heat energy change (Q) for the reaction between copper sulfate and water.
The mass of 1.0 cm3 of water is 1.0 g and the specific heat capacity of water is 4.2 J/g/°C.
Give your answer in kJ to 2 decimal places.
What type of reaction occurred between the copper sulfate and the water?
A student is investigating the energy change when a piece of magnesium ribbon is dropped into hydrochloric acid.
Write a balanced chemical equation for the reaction between magnesium (Mg) and hydrochloric acid (HCl) to form magnesium chloride and hydrogen.
The reaction results in energy being transferred to the surroundings.
Draw a reaction profile for the reaction between magnesium and hydrochloric acid.
The mass of hydrochloric acid used was 25 g.
The student recorded a temperature change of 8 °C.
Calculate the energy (Q) transferred due to the reaction.
The specific heat capacity of hydrochloric acid is 4.04 J/g/°C.
A student is investigating the energy released when using ethanol in a spirit burner.
The diagram below shows the student's apparatus.
Describe how the student could use the equipment in the diagram to find the heat released per gram of fuel burned.
The table below shows the student's results.
Calculate the energy released by the burner.
The specific heat capacity of water is 4.2 J/g/°C.
Another student calculates their theoretical temperature change to be 35°C. They only recorded a temperature change of 33°C.
Suggest why the temperature change recorded may be lower than the theoretical temperature change.
The table below shows how the molar enthalpy change varies for different alcohols.
Describe the relationship between molar enthalpy change and the number of carbon atoms per molecule of fuel.