PHYSICAL CHEM - ENERGETICS Flashcards
What is an endothermic reaction?
a reaction that absorbs heat energy from the surroundings
What is an exothermic reaction?
a reaction that releases heat energy into the surroundings
Is forming bonds exothermic/endothermic?
exothermic
Is breaking bonds exothermic/endothermic?
endothermic
What is enthalpy change (ΔH)?
the heat energy transferred in a reaction at constant pressure
Is the enthalpy change in endothermic reactions +ve/-ve?
ΔH is +ve
Is the enthalpy change in exothermic reactions +ve/-ve?
ΔH is -ve
What does ΔH° mean?
standard enthalpy change (reaction occurred under standard conditions)
What are standard conditions for a reaction?
- pressure = 100 kPa
- stated temp (usually 298 K)
- reactants and products in standard states
What is standard enthalpy change of formation (ΔfH°)?
the enthalpy change when 1 mole of a substance is formed from its constituent elements with all reactants and products in standard states under standard conditions
What is standard enthalpy change of combustion (ΔcH°)?
the enthalpy change when 1 mole of a substance is completely burned in O2 with all reactants and products in standard states under standard conditions
What is standard enthalpy change of neutralisation (ΔneutH°)?
the enthalpy change when 1 mole of water is formed in a reaction between an acid and an alkali under standard conditions
What is combustion calorimetry?
burning a sample and measuring temp rise of water to measure the amount of heat energy released
What is the equation that links heat energy required, mass, SHC and temp increase?
heat energy required (J) = mass (g) x SHC (J/kg°C) x temp increase (°C/K) (q = mCΔT)
What is the equation that links enthalpy change, heat energy and moles?
enthalpy change (kJmol^-1) = heat energy (J) / moles (mol) (ΔH = q/n)
