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INTRODUCTION: Purpose is to measure the change of temperature in water (DT) caused by the dissolving of an ionic salt and calculate the heat energy transferred to the water

DRIVING QUESTION: Is it possible to meausre heat exchange under conditions of constant pressure by using simple coffee cup calorimeter?

MATERIALS:

• Beakers, 400-mL, 2

• Styrofoam cups (that can be placed inside the 400-mL beaker), 2

• Thermometer/Temperature Probe with data-collection tools

• Graduated cylinder 50-mL

• Water

• Lithium chloride, 40 g

• Potassium chloride, 30 g

SAFETY PRECAUTIONS:

The reaction may produce enough heat to cause burns. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Review current Material Safety Data Sheets for additional safety, handling, and disposal information.

PROCEDURE:

1. Place the styrofoam cup inside a 400-mL beaker. This provides a stable base and a

receptacle for the reaction mixture if the foam cup breaks.

2. Measure and add 50 mL of water to the foam cup. Record the initial temperature of

the water. Either set up the temperature probe to collect the temperature every 5-10

seconds for about 2 minutes or manually record the highest/final temperature.

Add 40 g of lithium chloride to the water and start collecting temperature readings.

Note the maximum change in temperature.

3. Repeat Step 2 using 30 g of potassium chloride.

4. Compare the temperature changes during the dissolution of lithium chloride and

potassium chloride. c:

5. Discuss your observations, inferences, explanations and extensions.

DATA AND CONCLUSION:

At the beginning of the experiment the water's initial temperature was 23C then after adding the KCl and waiting 2 minutes, the temperature dropped to 15C. This shows that the KCL is endothermic since the temperature went down, it absorbed heat. When subtracting the last temperature from the first temperature, you get it's enthalpy, which in this case is 6. When experimenting with the LiCL, the initial temperature was 23C then increased to 76C after 2 minutes. Furthermore, since it released heat and it's enthalpy is higher than zero, LiCl resulted to be exothermic and having a higher heat capacity than KCl.

SCIENTIFIC PRINCIPLE:

Enthalpy (H) is the total energy of a system. The change in enthalpy (heat energy) of a process is symbolized by DH.

An exothermic process is one that release excess energy to the environment.

An endothermic process is one that absorbs energy from the environment in order to happen.

Solvation describes the process of polar water molecules being attracted to (and often surrounding) cations and anions of an ionic salt that is being dissolved (this releases free energy).

Dissolution (or dissolving) can be viewed as occurring in three steps. If sum of all these energies determines the overall energy properties of the process:

1. Breaking solute-solute attractions (endothermic), which is known as lattice energy in salts (ionic compounds).

2. Breaking solvent-solvent attractions (endothermic), for instance that of hydrogen bonding in water.

3. Forming solvent-solute attractions (exothermic), in solvation.