Lesson 6. Lesson 6: Calorimetry Lab

Carole Namowicz, Shruti Researcher
Chemistry
100 min
High School
v5

Overview

Students will utilize a calorimeter to measure the energy released in the following exothermic reaction:

Ca (s) + 2 H2O (l) → Ca(OH)2 (aq) + H2 (g)

The chemical reaction occurs when solid calcium metal is added to water, so the reaction can be set up to take place inside the calorimeter. Students will use three different quantities of calcium that they must test a minimum of three trials each. They will calculate the heat absorbed by the solution using the formula

qsolution = msolution • Cs solution • ∆T

msolution = mass of water + mass of calcium

Cs solution = specific heat of water

∆T = final temperature inside calorimeter – initial temperature inside calorimeter

The different quantities of calcium used will allow them to more accurately calculate the enthalpy of the reaction in kilojoules per mole.

This lab will require students write a formal lab report.

Standards

Next Generation Science Standards
  • Physical Science
    • [HS-PS1-4] Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
    • [HS-PS3-2] Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motions of particles (objects) and energy associated with the relative positions of particles (objects)
Computational Thinking in STEM
  • Data Practices
    • Collecting Data
    • Creating Data
    • Manipulating Data
    • Visualizing Data
    • Analyzing Data
  • Modeling and Simulation Practices
    • Assessing Computational Models
    • Using Computational Models to Understand a Concept
  • Systems Thinking Practices
    • Communicating Information about a System
    • Investigating a Complex System as a Whole
    • Thinking in Levels
    • Understanding the Relationships within a System

Activities

  • 1. Enthalpy of Reaction
  • 2. Calorimetry Lab Design Part 1: Reactant Amounts
  • 3. Calorimetry Lab Design Part 2: Procedure
  • 4. Calorimetry Experiment 1
  • 5. Calorimetry Experiment 2
  • 6. Calorimetry Experiment 3
  • 7. Enthalpy Calculations

Student Directions and Resources


In the last lesson you were introduced to calorimetry: an experimental method used to measure the transfer of heat within a closed system. You also learned that this transfer of heat is equal to the enthalpy change (∆H) which is the thermal energy transferred when bonds are broken or formed. You were able to explore how a calorimeter functions and determine the ideal material to use for your own calorimeter.

You will now use what you learned in the last lesson to design and execute your own calorimetry experiment.

You will need the following resources to complete this assignment.

1. Enthalpy of Reaction


Recall that overall chemical reactions can be categorized as endothermic or exothermic based on energy transferred into or out of the system. The chemical reaction is the system in this case.

Positive ΔH = energy moves into system from surrounding = endothermic

Negative ΔH = energy moves out system to surrounding  = exothermic

When a chemical reaction occurs, there is a characteristic change in enthalpy. The enthalpy change for a reaction is based on the overall balanced equation and is expressed in kilojoules per mole. This can be calculated using the same equation used to calculate enthalpy (q = m c ∆T), then dividing by the number of moles of a substance utilized.

The enthalpy of an exothermic reaction is shown below:

2 H2 (g) + O2 (g) → 2 H2O (g)   ΔH = -483.6 kJ/mol

This means that 483.6 kilojoules of energy are released for every two moles of hydrogen gas and one mole of oxygen gas that react to produce two moles of water vapor.


Question 1.1

Use the example exothermic reaction again shown here to answer the question below: 2 H2 (g) + O2 (g) → 2 H2O (g)   ΔH = -483.6 kJ/mol

How much energy would be released in the chemical reaction: 4 H2 (g) + 2 O2 (g) → 4 H2O (g)



Question 1.2

Use the example exothermic reaction again shown here to answer the question below: 2 H2 (g) + O2 (g) → 2 H2O (g)   ΔH = -483.6 kJ/mol

How much energy would be released in the chemical reaction: H2 (g) + ½ O2 (g) → H2O (g)

2. Calorimetry Lab Design Part 1: Reactant Amounts


The purpose of the lab is to measure the energy absorbed or released in a chemical reaction. You will utilize a calorimeter to measure the energy absorbed or released in the following chemical reaction:

Ca (s) + 2 H2O (l) → Ca(OH)2 (aq) + H2 (g)

In this reaction you have two reactants, calcium and water. The amount of calcium will be your independent variable. The amount of water will be a controlled variable, as you will keep it constant for all trials. Energy absorbed or released will be your dependent variable. Anything that is constant throughout your experiment is a controlled variable.

As you run your experiment, you will use three different amounts of calcium. You will run each trial three times, for a total of nine trials. The amount of water must be held constant throughout your experiment.


Question 2.1

Choose three different quantities of calcium in the range below and choose a set amount of water in the range below.

  • Range for amounts of calcium: 0.10 – 0.50 grams
  • Range for amount of water: 80.0 – 120.0 mL


Question 2.2

Calorimetry calculations will require that the quantity of water used be expressed as a mass rather than a volume. Your volume of water can be converted to a mass expressed in grams using the the density of water which is 1 g/mL. For example, if your volume of water is 50mL, that is equal to 50 g as 50g/50mL = 1 g/mL. Convert your volume of water to a mass in grams.



Question 2.3

Calorimetry calculations will also require the total mass of solution. Your solution is comprised of your solute (calcium) and your solvent (water). Thus, in order to calculate the mass of solution for each experiment you will add your mass of calcium to your mass of water for each experiment.

3. Calorimetry Lab Design Part 2: Procedure


Design an experiment to determine the enthalpy of reaction, ∆H°rxn, for the reaction of calcium metal with water by answering the questions below.


Question 3.1

Choose one of the following vessels in which you will conduct your calorimetry experiment.

  250 mL glass beaker and Parafilm to cover
  250 mL glass Erlenmeyer flask with a rubber stopper
  Aluminum can with no lid
  Styrofoam cups with plastic cover


Question 3.2

Explain the reasoning behind your choice of vessel in question 3.1



Question 3.3

In addition to the vessel you chose in question 3.1, you will be provided with the following materials: 

  • Calcium
  • Distilled water
  • 100 mL graduated cylinder
  • Temperature probe
  • Digital balance
  • Weighing Boats

Design a simple, repeatable procedure that you will follow for each of your three experiments below.

4. Calorimetry Experiment 1


Use the procedure you designed on pages 2-3 to complete three trials for your first decided upon amount of calcium to test.


Question 4.1

Fill in the data table below as you complete your three trials for experiment 1.



Question 4.2

Calculate averages for mass of calcium, mass of solution, and change in temperature below.

5. Calorimetry Experiment 2


Use the procedure you designed on page 2 to complete three trials for your second decided upon amount of calcium to test.


Question 5.1

Fill in the data table below as you complete your three trials for experiment 2.



Question 5.2

Calculate averages for mass of calcium, mass of solution, and change in temperature below.

6. Calorimetry Experiment 3


Use the procedure you designed on page 2 to complete three trials for your third decided upon amount of calcium to test.


Question 6.1

Fill in the data table below as you complete your three trials for experiment 3.



Question 6.2

Calculate averages for mass of calcium, mass of solution, and change in temperature below.

7. Enthalpy Calculations



Question 7.1

Fill in the data table below as you complete your experiment.

As the solution is composed primarily of water, the specific heat of the solution will simply be the specific heat of water:

*Cs solution = specific heat of water = 4.18 J/g•°C



Question 7.2

Classify the reaction as endothermic or exothermic using your enthalpy as evidence.



Question 7.3

Describe how thermal energy was transferred between the system and the surroundings. Include the terms "potential energy" and "kinetic energy" in your answer.



Question 7.4

Compare your calculated enthalpies for your three experiments. What kind of relationship exists between the amount of calcium utilized and the enthalpy?



Question 7.5

Compare your calculated enthalpies of reaction for your three experiments. What do you notice about these values?