Thermodynamic Properties Of Exothermic Reaction

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AIM
Design an experiment to study a thermodynamic property of a chemical substance, a chemical reaction, a physical change or chemical phenomenon.
BACKGROUND INFORMATION
Standard enthalpy change of solution, ∆Hsolnø, is the enthalpy change when one mole of a substance dissolves in water to form a solution of infinite dilution under standard conditions.1 The standard enthalpy change can either be exothermic or endothermic.
An exothermic reaction is a reaction where energy is released as a form of heat or light. This is usually denoted by a negative enthalpy change. The heat that is released in the reaction causes the surrounding temperatures to increase. Some exothermic reactions include corrosion, combustion, neutralization, decomposition and
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This is usually denoted by a positive enthalpy change. This indicates a gain in net energy. The heat that is absorbed in the system in the reaction causes the surrounding temperature to decrease. Some endothermic reactions include photosynthesis, melting of ice
1 Year 5 (2013) HL Chemistry Booklet, Topic 5, pg 24
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Energy
and cracking of alkanes. Below shows the energy profile diagram for an endothermic reaction.
Graph 1.2: Energy profile diagram for an endothermic reaction
Ea reactant product Progress of reaction
In this experiment, NaCl will be used. The dissociation equation is given as:
NaCl(s)!Na+(aq) + Cl–1(aq)
RESEARCH QUESTION
What is the enthalpy change of solution where a constant mass of 5g of sodium chloride is added to a constant volume of 100 cm3 of water by recording the change in temperature over time?
HYPOTHESIS
The enthalpy change would be endothermic.
TABLE OF VARIABLES
Independent Variable
Method of measurement
Time
A stopwatch is used to take time for each varied temperature reading. Each of the readings will be taken in intervals of 30 seconds. The total time taken would be 10
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Place the plastic Styrofoam cup lid on the Styrofoam cup.
2. Using an electronic mass balance, measure the mass of the Styrofoam cup with the lid.
Record the mass displayed.
3. Using the 100 cm3 measuring cylinder, measure 100 ml of water and pour it into the
Styrofoam cup with the lid. Record the new mass displayed.
4. Place the Styrofoam cup with the lid into the beaker.
5. Using the weighing bottle, measure out 5 g of NaCl powder.
6. Place the thermometer through the lid and record the temperature of the water, Tinitial.
7. Add the NaCl powder into the Styrofoam cup by removing the lid and quickly start the stopwatch. Place the lid back on the Styrofoam cup.
8. Record the temperature every 30 seconds for a total of 10 minutes.
Chemicals
Quantity
Sodium chloride powder (NaCl(s))
20 g
Water
500 ml
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9. Repeat steps 4 to 8 for a total of 3 recordings. Making sure that all the apparatus are washed thoroughly before each experiment.
10. Draw a graph for Tavg/ oC against time/ s and extrapolate the final temperature, tfinal. 11. Calculate the enthalpy change of solution, ∆Hsoln.
RESULTS
Data

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