Measurement of an Enthalpy Change

Measurement of an Enthalpy Change

Enthalpy change (ΔH) is the heat energy change that occurs during a chemical reaction at constant pressure. It tells us whether heat is released to the surroundings or absorbed from them.

Casual Bangla explanation (short)

সহজভাবে বললে, বিক্রিয়ার সময় পরিবেশ গরম হচ্ছে নাকি ঠান্ডা হচ্ছে— এই তাপের পরিবর্তনটাই হলো enthalpy change।

How is Enthalpy Change Measured?

• The reactants are mixed in a calorimeter (often a polystyrene cup).
• The reaction causes a change in temperature.
• The temperature change (ΔT) is recorded using a thermometer.
• The heat energy change is calculated using a standard formula.

$$q=m\times c\times \Delta T$$

Where:

• q = heat energy change (J)
• m = mass of the solution (g)
• c = specific heat capacity (4.18 J g⁻¹ K⁻¹ for water)
• ΔT = change in temperature (final − initial)

Formula in simple Bangla

তাপমাত্রা যত বেশি বদলাবে এবং ভর যত বেশি হবে, তাপের পরিবর্তনও তত বেশি হবে।

Types of Enthalpy Change

• Exothermic reaction: Temperature increases; heat is released (ΔH is negative).
• Endothermic reaction: Temperature decreases; heat is absorbed (ΔH is positive).

Easy memory trick

Temperature rises → heat released → exothermic
Temperature falls → heat absorbed → endothermic

Exam Tip: Always calculate ΔT correctly (final − initial) and express the enthalpy change per mole of reactant.