Unit 18 A: Enthalpy and Entropy

Unit 18: Industrial Chemical Reactions
Learning aim A: investigate chemical thermodynamics in order to understand
spontaneous reactions
Enthalpy and Entropy


The objective of this project was to conduct the following investigation to
demonstrate the accurate measurement of enthalpy changes.
Calculations of the various enthalpy changes had to be calculated in kJ per
mole based on the temperature changes measured for. Practical were the
dissolution of anhydrous sodium carbonate in water, the dissolution of
ammonium chloride in water, and the neutralization of hydrochloric acid
and the combustion of alcohol.


Equipment
 Hydrochloric acid solution
 Sodium hydroxide solution
 Polystyrene cup
 Thermometer
 Distilled/deionised water
 Burette
 Pipette
 Pipette filler
 Small funnel
 Lab coat
 Safety glasses


Health and safety assessment

 Hydrochloric acid solution is irritant and corrosive. It can cause serious damage or injury
if comes in contact with skin or eyes. If inhaled, it might cause irritation in the nose eye
and respiratory tract.
 Sodium hydroxide solution is irritant and can cause diarrhea, vomiting and chest or
stomach pain if inhaled or eaten.

, Lab coat must be worn as a health and safety measure to protect from acid spillages
 Gloves must be worn to protect the hand from acid irritation as it can cause serious
damage if comes in contact with the skin
 Googles must be worn to protect the eyes as the acid is dangerous and can cause
irritation to severe injury or blindness.

Method

 Rinse a burette with the hydrochloric acid provided. Set up the burette and, using a
funnel, fill it with the hydrochloric acid -
 Using the burette, transfer 25.0 cm of the hydrochloric acid to a clean, dry beaker.
 Measure the temperature of the hydrochloric acid in the beaker to one decimal place.
Record your result
 Rinse the thermometer with distilled or de-ionised water and dry the thermometer.
 Rinse a pipette with the sodium hydroxide solution provided. Using this pipette and 3 a
filler, transfer 25.0 cm³ of the sodium hydroxide solution to a clean, dry polystyrene cup.
 Place the polystyrene cup containing the sodium hydroxide solution in a beaker to
provide support and additional insulation, Mount the thermometer in the cup using a
clamp stand. The bulb of the thermometer must be fully immersed in the solution and
should not touch the sides of the cup. Place a stirrer in the cup.
 Stir the sodium hydroxide solution in the cup and measure the temperature to one
decimal place. Draw a table to record your results. Every minute for a further three
minutes, stir the solution, measure the temperature, and record each result in the table.
 At the fourth minute add the 25,0 cm of hydrochloric acid from the beaker. Stir the
mixture but do not record the temperature.
 Continue to stir the mixture, and measure the temperature at the fifth minute, and then
every subsequent minute up to ten minutes. Record each temperature to 1 decimal
place in the table.

Time (in minutes) Temperature
1 25
2 25
3 25

, 4
5 28
6 28
7 28
8 27
9 27
10 27



Graph




Results and calculations

Working out the heat enthalpy and energy change:

q=m x c x ∆t



q= 50 x 4.18 x 3 = 627J



Moles of sodium hydroxide (NaOH) = 0.0125 mols




Moles of hydrochloric acid (HCI) = 0.125 mols