Featured in PASCO’s Chemistry through Inquiry Teacher Guide

Chemistry through Inquiry Teacher Guide

(PS-2871C)

Features over 25 inquiry based labs covering the fundamental concepts of lab skills, structure & properties of matter, chemical reactions and more.

Hess's Law

Lab Summary

Use a temperature sensor to show that the change in enthalpy for the reaction between solid sodium hydroxide and aqueous hydrochloric acid can be determined using both a direct and an indirect method.

Theory

Show that the change in enthalpy for the reaction between solid sodium hydroxide and aqueous hydrochloric acid can be determined using both a direct and an indirect method. Through this investigation, students:

  • Measure initial and final temperatures and use the calculated temperature difference to determine the enthalpy change ΔH.
  • Confirm that the overall heat evolved or absorbed in a chemical process is the same whether the process takes place in one or several steps (Hess's law).
  • Explain that directly measuring the heat evolved or absorbed in a chemical process is not always possible for a variety of reasons. Reasons include reactions that are too fast or too slow, are explosive, or involve toxic or expensive materials.

Method

Students conduct the following procedures:

  • Measure temperature changes when chemicals are mixed.
  • Calculate molar enthalpies directly and indirectly using Hess's law.
  • Compare calculated molar enthalpies using direct and indirect measurements.

Sensors / Equipment Used:

PASPORT Chemistry Sensor

(PS-2170)

Allows students to measure Temperature, pH/ISE/ORP, Absolute Pressure & Voltage in one sensor. For use with PASPORT Interfaces.

Materials Used:

Beaker, 250-mL 
Graduated cylinder, 50-mL 
Spatula 
Polystyrene cup - 2
Lid for polystyrene cup 
Weighing paper - 2
Wash bottle and waste container 
1.0 M Hydrochloric acid - 25 mL
0.5 M Hydrochloric acid - 50 mL
1.0 M Sodium hydroxide - 25 mL
Sodium hydroxide pellets - 2.0 g
Distilled (deionized) water - 50 mL

Your Bundle Options:

Option 1:

Chemistry Starter Sensor Bundle

(PS-2921)

A sensor bundle specifically designed to get you started using probeware in your chemistry lab. Also: perform 22 Lab Activities from Chemistry through Inquiry teacher guide.

Option 2:

Chemistry Standard Sensor Bundle

(PS-2927C)

Contains the sensors and probes needed to perform all 17 experiments in the Advanced Chemistry Teacher Guide and all 25 labs in the Chemistry through Inquiry Guide.

Interface Required

This experiment may require software and an interface for data collection.