Thermochemistry: determining the heat of reaction

Objectives

1. To determine the value of heat capacity of a calorimeter.

2.  To determine the heat of neutralization of HCl and NaOH.

Introduction

The Study of energy changes which take place during a chemical reaction is called thermochemistry or chemical energetic. Every chemical changes are accompanied by the evolution or absorption of heat, although in many cases this is not obvious as the amount is so small that no noticeable change in temperature occurs.
The heat can be measure by using calorimeter.
1.     The rises in temperature when a substance is heated depend on the heat capacity of the substance.
2.    The molar heat capacity of a substance is the energy required to raise the temperature of one mole of the substance by one kelvin.
3.    The specific heat capacity of a substance is the energy required to raise the temperature of 1 gram of the substance by one kelvin. For example, the specific heat capacity for water is 4.18 J g-1 K-1. This means that to raise 1g of water from T K to (T + 1) K requires 4.18 J of heat energy.
4.    The enthalpy change of reaction involving solutions can be calculated by the following equation

H = mc  T

Where   H = heat absorbed or liberated

C = Specific heat capacity

M = mass of solution

 T = the increase or decrease in temperature

Equipment
#     Stop watch
#     Calorimeter
#     Conical flask
#    Thermometer
#    100 ml beaker
#    Measuring cylinder
#    Bunsen burner

Reagent
 #  NaOH 1.0 M
# HCl 1.0 M
 # Distilled Water

Procedure

A.    

Determination of the heat capacity of a calorimeter

1.    The temperature of an empty calorimeter was measured by putting a thermometer inside the calorimeter, T1

2.    50 ml of distilled water poured into 100ml beaker.

3.    The beaker was heated to a temperature between 50°C to 60°C.

4.    Hot water poured into the calorimeter. The initial temperature of the hot water was taken immediately, T2.

5.    The decrease in temperature observed until it stays constant for a few minutes. The temperature was recorded, T3.


 Determination of the heat neutralization of HCl 1.0 M and NaOH 1.0M

1.    25 ml NaOH 1.0M and 25 ml HCl 1.0M was measured by using measuring cylinder.

2.    The NaOH Solution was poured into the calorimeter and the HCl solution into a conical flask. Record the initial temperature of each solution.

3.    Without removing the thermometer, the cover was lifted slightly and quickly poured all the HCl solution into the calorimeter.

4.    The cover of the calorimeter was quickly replaced.

5.    The solution was stirred and begun record the temperature every 15 seconds for 2 minutes.

6.    The experiment was repeated twice.

Result

A)   Determination of the heat capacity of a calorimeter

i)              T1 = 29°C

ii)             T2 = 64°C

iii)            T3 = 53°C

B)   Determination of the heat of neutralization of HCl 1.0M and NaOH 1.0M.

First experiment

Initial temperature of NaOH = 28°C

            Initial temperature of HCl = 28°C

Time(s)	Temperature(°C)
15	35
30	34
45	34
60	34
75	34
90	34
105	34
120	34

Table of NaOH + HCl for 2 minutes

Second Experiment

Initial temperature of NaOH = 28°C

            Initial temperature of HCl = 28°C

Time(s)	Temperature(°C)
15	35
30	34
45	34
60	34
75	34
90	34
105	34
120	34

Table of NaOH + HCl for 2 minutes