Chemistry52 views·Updated Jun 21, 2026·2 pages

Chemistry Basics: Understanding Energetics

Aliki 🩵@study_wabbit

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Chemical reactions are all about energy changes - some release...

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SECTION 5:
ENERGETICS
Chemical Reactions:
liks Lagoudaki
*Bonds are broken, which absorbs energy
*New bonds are made, which releases energy

Energy Changes in Chemical Reactions

Every chemical reaction involves breaking old bonds (which needs energy) and forming new bonds (which releases energy). The overall energy change depends on which process requires more energy.

Exothermic reactions happen when more energy is released making new bonds than is needed to break the old ones. You'll notice the temperature rising because energy transfers from the chemicals to the surroundings. Common examples include combustion, displacement reactions, and neutralisation.

Endothermic reactions are less common but equally important. Here, more energy is absorbed breaking bonds than is released forming new ones. The temperature drops as energy is absorbed from the surroundings into the chemicals. Think photosynthesis and thermal decomposition.

Key Point: The enthalpy change (ΔH) tells you the energy change per mole - it's negative for exothermic reactions and positive for endothermic ones.

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Measuring and Calculating Energy Changes

To measure enthalpy changes experimentally, you'll use a simple calorimeter setup with a polystyrene cup, thermometer, and insulating lid. The key is minimising heat loss to get accurate results.

The essential equation is q = mcΔT, where q is heat energy, m is mass of solution, c is specific heat capacity $4.2 J/g°C for water$ , and ΔT is temperature change. Then calculate ΔH = q ÷ moles.

For enthalpy of combustion experiments, you burn a fuel to heat water and measure the temperature rise. Improve accuracy by using heat shields, reducing distances between burner and beaker, and covering everything to prevent heat loss.

Watch Out: Your experimental values will often be lower than theoretical ones because heat gets lost to the equipment and surroundings - this is completely normal!

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Chemistry52 views·Updated Jun 21, 2026·2 pages

Chemistry Basics: Understanding Energetics

Aliki 🩵@study_wabbit

Add to Google sources

Chemical reactions are all about energy changes - some release heat whilst others absorb it from their surroundings. Understanding these energy transfers is crucial for predicting how reactions behave and calculating the exact amounts of energy involved.

of 2

Energy Changes in Chemical Reactions

Key Point: The enthalpy change (ΔH) tells you the energy change per mole - it's negative for exothermic reactions and positive for endothermic ones.

of 2

Measuring and Calculating Energy Changes

To measure enthalpy changes experimentally, you'll use a simple calorimeter setup with a polystyrene cup, thermometer, and insulating lid. The key is minimising heat loss to get accurate results.

Watch Out: Your experimental values will often be lower than theoretical ones because heat gets lost to the equipment and surroundings - this is completely normal!