By Amber Webb | Updated Aug 30, 2022
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In chemistry, the heat of combustion quantifies the energy released when a substance undergoes complete oxidation. Determining this value for common fuels—such as paraffin wax—provides insight into energy conversion processes, from vehicle engines to the calories in our diet. This practical experiment uses readily available materials to measure the heat of combustion of a paraffin candle, offering a hands‑on understanding of thermochemical principles.
Fill an empty soda can with exactly 100 mL of cool water. Suspend a digital thermometer in the water using a strip of Sticky Tack so that it does not touch the can’s walls. This arrangement constitutes a simple calorimeter.
Trim the top of a second soda can to leave a 1–2 inch-wide disc. Weigh the disc and record its mass. Weigh the paraffin candle, then place the candle on the disc inside the calorimeter.
Measure the initial water temperature. Light the candle, then lift the calorimeter with tongs so the flame is just above the candle, ensuring adequate airflow. Keep a safe distance to avoid burns.
When the flame extinguishes, note the maximum water temperature. Remove the candle and disc, weigh the remaining candle mass, and subtract the disc mass to obtain the mass of the wax that combusted.
Mass burned = initial candle mass – final candle mass.
ΔT = final temperature – initial temperature.
Assuming 1 mL of water ≈ 1 g, the experiment uses 100 g of water. The specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹.
Thermal energy (Q) = 100 g × ΔT × 4.18 J g⁻¹ °C⁻¹.
Heat of combustion (ΔH_comb) = Q ÷ mass burned (g). The result is expressed in J g⁻¹.
Do not touch the calorimeter while it is hot or immediately afterward. Use tongs and maintain a safe working distance to prevent burns.
