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LESSON PLAN in Hess S Law. Last updated October 17, 2016.

Lesson Plan

Summary

In this lesson, students learn about the concepts of Hess's Law and how to solve problems involving them.

Grade Level

High school

Objectives

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

  • Understand the concepts behind Hess’s Law.
  • Be able to solve problems using Hess’s Law.

Chemistry Topics

This lesson supports students’ understanding of

  • Hess’s Law
  • Enthalpy

Time

Teacher Preparation: 10 minutes

Lesson: 30 minutes

Materials

  • PowerPoint

Safety

  • No specific safety precautions need to be observed for this activity.

Teacher Notes

  • Students get really involved in this lesson because they view each reaction set as if it were a puzzle.
  • Included in the downloads section is an accompanying worksheet (and answer key) with six problems for students to practice what they’ve learned from the lesson.
Downloads

Submitted by
Karen DiLollo
Bridgewater-Raritan High School
Bridgewater, New Jersey

For the Student

Directions:  Using Hess’s law, indicate on the line what change is made to the equation and rewrite each equation to find the ΔH for each given reaction.

1.   Calculate the ΔH for the reaction

2 Al(s)  +  Fe2O3(s)  → 2 Fe(s)  +  Al2O3(s)

Given the following information:

______       2 Al(s)   +  3/2 O2(g) → Al2O3(s)                    ΔH = -1670 kJ/mol

______       2 Fe(s)  +  3/2 O2(g)  → Fe2O3(s)                    ΔH = -824 kJ/mol

 

2.   Calculate the ΔH for the reaction

2 H2O2(l)  →  2 H2O(l)  +  O2(g)

Given the following information:

______       H2(g)  +  O2(g)  →  H2O2(l)                              ΔH = -188 kJ/mol

______       H2(g)  +  ½ O2(g)  →   H2O(l)                           ΔH = -286 kJ/mol

 

3.   Determine the ΔH for the reaction

NO(g)  +  ½ O2(g)  →  NO2(g)

Given the following information:

______       ½ N2(g)  +  ½ O2(g)  →  NO(g)                         ΔH = +90.0 kJ/mol

______       ½ N2(g) +  O2(g)  →  NO2(g)                           ΔH = +34.0 kJ/mol

 

4.   Calculate the ΔH for the reaction

Cu(s)  +  ½ O2(g)  →  CuO(s)

Given the following information:

______       CuO(s)  +  Cu(s)  →  Cu2O(s)                          ΔH = -11 kJ/mol

______       2 CuO(s) →  Cu2O(s)  +  ½ O2(g)                    ΔH = +115 kJ/mol

 

5.   Calculate the ΔH for the reaction

PbCl2(s)  +  Cl2(g)  →  PbCl4(l)

Given the following information:

______       Pb(s)  +  2 Cl2(g)  →  PbCl4(l)                          ΔH = -393 kJ/mol

______       Pb(s)  +  Cl2(g)  →  PbCl2(s)                             ΔH = -359 kJ/mol

 

6.   Calculate the ΔH for the reaction

N2(g) +  O2(g)  →  2 NO(g)

Given the following information:

______       4 NH3(g)  +  3 O2(g)  →  2 N2(g)  +  6 H2O(l)       ΔH = -1530 kJ/mol

______       4 NH3(g)  +  5 O2(g)  →  4 NO(g)  +  6 H2O(l)      ΔH = -1170 kJ/mol

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