Understanding Energy Changes in Reactions
Ever wondered why some reactions make things hot whilst others cool them down? Exothermic reactions release energy to their surroundings, making the temperature drop and giving a negative ΔH value. Think of combustion or neutralisation - they're making new bonds and releasing energy.
Endothermic reactions do the opposite - they absorb heat from their surroundings, causing temperature to rise and giving a positive ΔH. Thermal decomposition is a classic example where you're breaking bonds and need energy input.
Enthalpy change (ΔH) measures this heat energy at constant pressure under standard conditions (100kPa pressure, 298K temperature). You'll use the formula q = mcΔT constantly - it's your best friend for calculations. Remember: mass × specific heat capacity × temperature change gives you the energy transferred.
Key Point: Standard conditions are crucial - always check you're using 100kPa and 298K when dealing with standard enthalpy values.
