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Exothermic and Endothermic Lab (11 Favorites)

LAB in Exothermic & Endothermic. Last updated June 6, 2018.


Summary

In this lab, students determine whether mixing two chemicals is endothermic or exothermic. One is a physical change, one is a chemical change.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

  • identify reactions as either endothermic or exothermic.
  • write balanced chemical equations including heat energy.

Chemistry Topics

This lesson supports students’ understanding of

  • Endothermic/exothermic reactions
  • Chemical changes

Time

Teacher Preparation: 10–15 minutes

Lesson: 40 minutes

Materials

For each group:

  • NH4Cl powder
  • Water bottle
  • Thermometer
  • Balance
  • Test tubes
  • Spatula
  • Weigh boat
  • 10-mL graduated cylinder
  • Zinc metal
  • HCl

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Students should be reminded to handle acid carefully. If any gets on their skin, they should alert you and immediately flush the area with water.

Teacher Notes

  • This is a quick, simple lab that allows students to witness endothermic and exothermic processes; one from a physical change, one from a chemical change.

For the Student

Lesson

Background

In chemical and physical changes, energy can be transferred to or from the surroundings. For example, when a fire burns, it transfers heat energy to the surroundings. Objects near a fire become warmer and the temperature rises. In this experiment, you will make observations and evaluate whether heat energy is released or absorbed.

Purpose

To determine whether a process is exothermic or endothermic.

Safety

  • Always wear safety goggles when working with chemicals in a laboratory setting.
  • Handle acid carefully. If any gets on your skin, alert your teacher and immediately flush the area with water.

Materials

  • NH4Cl
  • Water
  • Thermometer
  • Balance
  • Test tubes (2)
  • Weigh boat
  • 10-mL graduated cylinder
  • Zinc
  • <1.0-M HCl

Procedure

Part I

  1. Measure 5.0 mL of distilled water. Pour the water into a test tube.
  2. Find the temperature and record in your data table.
  3. Measure 1.0 g of NH4Cl. Place your sample into the test tube with the water.
  4. Measure the final temperature and complete your data table.

Part II

  1. Measure 5.0 mL of hydrochloric acid. Pour the acid into a test tube.
  2. Find the temperature and record in your data table.
  3. Add a small piece of zinc to the hydrochloric acid. Gently stir until all zinc has reacted.
  4. Measure the final temperature and record it in your data table.

Data

Part I

Initial temperature, T1 °C
Final temperature, T2 °C
Change in temperature, DT °C

Part II

Initial temperature, T1 °C
Final temperature, T2 °C
Change in temperature, DT °C

Analysis

  1. Did you observe a physical or chemical change when you added NH4Cl to the distilled water? Describe the evidence to support your answer.

  2. Did you observe a physical or chemical change when you added zinc metal to hydrochloric acid? Describe the evidence to support your answer.

  3. When you added NH4Cl to distilled water, that was an (endothermic / exothermic) process and energy was (absorbed / released) by the system. Explain.

  4. When you added zinc metal to hydrochloric acid, that was an (endothermic / exothermic) process and energy was (absorbed / released) by the system. Explain.

  5. What you observed in part I is NH4Cl(s) → NH4+(aq) + Cl-(aq) ΔH = 20 kJ/mol
    Rewrite this equation with the heat energy on the reactant or product side.

  6. What you observed in part II is Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
    Is its ΔHrxn positive or negative? Explain.

  7. Draw the general potential energy diagram for each part.

Part I

Part II