Measuring Heat Energy in Acid-Base Reactions: A Practical Guide to Enthalpy of Neutralisation
Expert reviewed •22 November 2024• 5 minute read
Introduction
When acids and bases react, they produce water and release heat energy. This heat release is known as the enthalpy of neutralisation - a key concept in the HSC Chemistry curriculum that demonstrates the energy changes in chemical reactions.
Understanding Enthalpy of Neutralisation
The enthalpy of neutralisation (ΔH) is defined as the energy released when one mole of water is formed from the complete reaction between an acid and a base. This reaction is exothermic, meaning it releases heat to its surroundings, resulting in an increase in the solution's temperature.
Measuring Energy Changes Using Calorimetry
Calorimetry is a technique that measures heat energy changes in chemical reactions by tracking temperature changes in a controlled environment. The energy absorbed by the solution (q) can be calculated using the equation:
q=mcΔT
Where:
q = heat energy absorbed by solution (Joules, J)
m = mass of final solution (kilograms, kg)
c = specific heat capacity (J kg⁻¹ K⁻¹)
ΔT = temperature change (Kelvin or °C)
The Role of Specific Heat Capacity
Specific heat capacity (c) represents the energy needed to raise the temperature of 1 kg of a substance by 1 Kelvin. For water, this value is:
cwater=4.18×103 J kg−1 K−1
Calculating Molar Enthalpy Change
The enthalpy change of neutralisation (ΔH) is calculated using:
ΔH=−nq
Where:
ΔH = enthalpy change of neutralisation (kJ mol⁻¹)
q = heat energy absorbed by solution (J)
n = number of moles of water formed
Negative sign indicates energy release
Experimental Considerations
Key Assumptions
No heat loss to surroundings
Equal initial temperatures of acid and base solutions
Solution's specific heat capacity approximates that of water
Improving Accuracy
To enhance experimental accuracy:
Use insulation (e.g., styrofoam) around the calorimeter
Cover the reaction vessel
Use a calibrated thermometer
Ensure rapid mixing of solutions
Record temperature at regular intervals
Common Sources of Error
Heat loss to surroundings
Heat absorption by calorimeter
Incomplete mixing
Inaccurate temperature readings
Solution concentration variations
Remember that experimental values will typically differ from theoretical values due to these factors.