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.

Lesson Plan

Students will be able to

describe the setup of calorimetry experiments,
understand the different types of reactions that calorimetry can be used for,
identify problems with described calorimetry experiments and explain their effects on the results,
use experimental values and the formula to calculate , the heat energy transferred,
calculate the values of , , , or when the other values are given,
use tabulated or graphical data to calculate , where and are already known (e.g., reactions in water),
calculate the molar enthalpy change, , from the heat energy transfer, .

Lesson Video

Lesson Explainer

Lesson Worksheet

Q1:

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?

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 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.

Q2:

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 What is the molar enthalpy change for each mole of consumed? Give your answer as a whole number.

Q3:

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.