# Worksheet: Measuring Enthalpy Changes

In this worksheet, we will practice performing calorimetry experiments and using the results to calculate the enthalpy change for a chemical reaction.

Q1:

The diagram below shows the experimental setup for a simple calorimeter to measure the enthalpy change in certain reactions. For which type of reaction would this experimental apparatus not be suitable for measuring the change in enthalpy?

• BCombustion
• CDisplacement
• DNeutralization
• EPrecipitation

Q2:

Which of the following statements best describes what calorimetry is?

• AThe measurement of the change in the number of degrees of freedom that a system has
• BThe amount of heat needed to raise the temperature of 1 gram of a substance by
• CThe amount of energy needed to break one mole of bonds
• DThe amount of energy produced by the combustion of an item of food
• EThe measurement of the amount of heat energy transferred in or out of a system during a chemical or a physical change

Q3:

The diagram below shows the experimental apparatus for a combustion calorimeter.

Why is a copper container used in this calorimeter?

• ACopper is a good conductor of heat and allows efficient energy transfer of heat to the water.
• BCopper is malleable and can easily be shaped.
• CCopper is a good conductor of electricity.
• DCopper has a high melting point and so is not affected by the heat of the flame.
• ECopper does not react with the water, preventing any chemical reactions from occurring.

Why is the experimental apparatus surrounded by draught excluders?

• ATo protect the calorimeter from vibrations
• BTo prevent the fuel or the water from being evaporated
• CTo prevent the wind from blowing out the flame
• DTo reduce the amount of heat lost to the surroundings
• ETo keep the pressure inside the calorimeter constant

Q4:

A student wants to take 150 mL of water at and boil it. They are given some fuel that produces 6.75 kJ of heat energy per 1 g of fuel burned. How much fuel does the student need to burn in order for the water to reach its boiling point? Give your answer to the nearest whole number. Assume the heat capacity of water remains constant.

Q5:

In an experiment, 14.9 g of potassium chloride was added to 150 mL of water at . The change in temperature was recorded and is shown in the graph below.

By drawing a line of best fit between the data points from 0 to 40 seconds, which of the following is the temperature at 40 seconds?

• A
• B
• C
• D
• E

By drawing a line of best fit between the data points from 75 to 120 seconds and extrapolating, which of the following is the temperature at 40 seconds?

• A
• B
• C
• D
• E

Using the two lines of best fit, calculate the change in temperature at 40 seconds.

Determine the value of for this reaction, taking the specific heat capacity of water to be . Give your answer in units of kilojoules per mole and to 1 decimal place. Remember to include a sign in your answer.

Q6:

A student sets up an experiment using calorimetry to measure the enthalpy change of a neutralization reaction. Instead of a polystyrene cup, the student decides to use a glass beaker. How will this affect the results of the experiment?

• AThe reaction will be quicker in the glass beaker, causing the change in temperature to be quicker.
• BThe temperature change will be higher, as the glass beaker is more insulating than the polystyrene cup.
• CThe temperature change will be lower, as more heat will be lost through the glass beaker to the surroundings.
• DThe beaker has a higher mass than the polystyrene cup, so the amount of heat energy transferred will be greater.
• EThe increase in temperature will cause the glass beaker to crack.

Q7:

When burned, 40.1 g of methane () was found to raise the temperature of 10 kg of water by . What is the molar enthalpy change, to the nearest whole number, for the combustion of methane? Take the specific heat capacity of water to be .

Q8:

Why will the measured change in energy always be lower than the total energy transferred?

• ASome of the energy gets destroyed during the reaction.
• BThe thermometers will have an error associated with them.
• CThere will always be some amount of heat energy lost to the surroundings.
• DNot all of the reactants will be used up.
• EThe water will contain impurities that will absorb some of the heat energy.

Q9:

When 50 mL of water containing 0.5 M at was mixed with 50 mL of water containing 0.5 M at , the highest temperature recorded was .

What is the value of for this reaction? Use a value of for the specific heat capacity of water. Give your answer in joules.

If is the limiting reagent, what is the value of in kilojoules per mole of ?

The balanced equation for the reaction is shown below. What is the molar enthalpy change for each mole of consumed? Give your answer as a whole number.

Q10:

The experimental setup for a simple calorimeter is shown below.

Why does the calorimeter need to have a lid?

• ATo stop debris from falling into the reaction mixture
• BTo hold the thermometer in place
• CTo prevent the reaction mixture from being spilled
• DTo prevent the air from reacting with the mixture
• ETo reduce the loss of heat energy through evaporation

Why is the polystyrene cup placed into a beaker of cotton wool?

• ATo prevent the glass beaker from breaking
• BTo help catalyze the reaction
• CTo hold the polystyrene cup in place
• DTo increase insulation and prevent heat loss to the surroundings
• ETo stop the reaction mixture from leaking out of the polystyrene cup

Q11:

An experiment is carried out using calorimetry to compare the heat released from a range of different fuels. Which of the following factors does not need to be kept constant when repeating the experiment for each different fuel?

• ASame mass of fuel burnt
• BThermometer
• CVolume of the water
• DStarting temperature of the water
• ESame burner and wick

Q12:

In an experiment, 80 g of water was measured, placed into a copper container, and its temperature recorded. A spirit lamp containing a fuel was weighed and then placed underneath the copper container. The wick of the spirit lamp was lit, and the water was heated until the temperature reached . The flame was then extinguished, and the final temperature of the water was recorded. The spirit lamp was then also weighed. The results are listed in the table below.

 Initial temperature of water (∘C) Final temperature of water (∘C) Mass of spirit lamp before heating (g) Mass of spirit lamp after heating (g) 22.5 51.2 54.38 52.88

What is the value of , the heat energy transferred, in the experiment? Give your answer in units of kilojoules and to 1 decimal place. Use a value of for the specific heat capacity of water.

What is the heat change per gram of fuel? Give your answer in units of kilojoules per gram of fuel.

• A2.2 kJ/g of fuel
• B14.4 kJ/g of fuel
• C8.1 kJ/g of fuel
• D11.4 kJ/g of fuel
• E6.4 kJ/g of fuel

Q13:

Which of the following equations can be used with the results from a calorimetry experiment to calculate the heat energy transferred during a chemical reaction?

• A
• B
• C
• D
• E

Q14:

A student is setting up an experiment to measure the enthalpy change in a neutralization reaction between hydrochloric acid and potassium hydroxide. Before mixing the two solutions together in a polystyrene cup, the student places a beaker of each solution in a water bath set to . Why does the student do this?

• ATo ensure the reactants have the correct activation energy needed to react
• BTo make the solutions less viscous
• CTo ensure both solutions are at the same temperature as each other
• DTo increase the rate of reaction between the hydrochloric acid and the potassium hydroxide
• ETo remove any impurities in the solutions