Lesson: Measuring Enthalpy Changes Chemistry

In this lesson, we will learn how to perform calorimetry experiments and use the results to calculate the enthalpy change for a chemical reaction.

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15:24

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Lesson Worksheet

Q1:

In an experiment, 14.9 g of potassium chloride was added to 150 mL of water at 22C . 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?

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?

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

Determine the value of Δ𝐻 for this reaction, taking the specific heat capacity of water to be 4.2/JgC. Give your answer in units of kilojoules per mole and to 1 decimal place. Remember to include a sign in your answer.

Q2:

When 50 mL of water containing 0.5 MHSO24 at 20C was mixed with 50 mL of water containing 0.5 MNaOH at 20C , the highest temperature recorded was 26C .

What is the value of 𝑞 for this reaction? Use a value of 4.2/JgC for the specific heat capacity of water. Give your answer in joules.

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

The balanced equation for the reaction is HSO()+2NaOH()NaSO()+2HO()24242aqaqaqaq What is the molar enthalpy change for each mole of HSO24 consumed? Give your answer as a whole number.

Q3:

A student wants to take 150 mL of water at 25C 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.

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