Reactions with Heat Transfer

Reactions with Heat Transfer

Changes in matter involve changes in energy. Reactions with heat transfer are either exothermic or endothermic. The enthalpy of reaction (H) is similar to heat – it is the energy released or absorbed in a chemical reaction. Energy that is released in an exothermic reaction has a negative enthalpy value in Joules. Energy that is absorbed in an endothermic reaction has a positive enthalpy value in Joules. Heat/enthalpy is not to be confused with temperature.

Purpose: The purpose of this experiment is to examine reactions with heat transfers, become familiar with thermometers, and practice generating graphs from data.

Materials: waterthermometer25 mL graduated cylinder

sodium hydroxidefoam cupclock

ammonium chloridebalance

Procedure: (Part A and B can be done in any order)

Part A:1. Mass a foam cup. Fill with about 25 mL of water and record the mass

of the water used along with the initial temperature with proper sid digs.

2. Add about 1 gram of sodium hydroxide to the water in the cup and

immediately record the temperature every 30 seconds for 5 minutes.

3. Pour the solution down the sink.

4. Repeat steps 1 – 3 for a second trial.

Part B:1. Mass a foam cup. Fill with about 25 mL of water and record the mass

of the water used along with the initial temperature with proper sid digs.

2. Add about 3 grams of ammonium chloride to the water in the cup and

immediately record the temperature every 30 seconds for 5 minutes.

3. Pour the solution down the sink.

4. Repeat steps 1 – 3 for a second trial.

Data: Prepare a data table on the back of this sheet with all quantitative data.

Analysis: Graph the four trials on the graph paper with temperature on the y-axis (vertical) and time of the x-axis (horizontal). Be sure to title your graph, name each axis, and label the units.

Conclusions: Questions to come later in lecture after a post lab discussion.

Reactions with Heat Transfer LabName:______

Conclusions: Use complete sentences where applicable. Don’t forget work, units, and proper sig digs for mathematical problems.

1. When the ammonium chloride was added to the water, was the reaction exothermic or endothermic? Explain how you know.

2. When the sodium hydroxide was added to the water, was the reaction exothermic or endothermic? Explain how you know.

3. How much heat was gained or lost in the ammonium chloride reaction? Use your best trial’s data.

4. How much heat was gained or lost in the sodium hydroxide reaction? Use your best trial’s data.

5. Convert 24.0 J to cal:

6. Convert 60.40 mcal to J:

7. Convert 0.28 cJ to kcal:

8. 650 g of water is heated with 9600 J of heat, what will be the temperature change in degrees Celsius?

9. What is the mass in grams of a sample of water if it takes 13.9 kJ of energy to raise the temperature from 25.2 oC to 28.7oC?