2 - Energetics Flashcards
Enthalpy Change
Amount of heat energy taken in or given out during any change in a system provided the pressure is constant.
What are standard conditions?
298K, 100kpa solutions at 1mol dm-3
What is the standard enthalpy change of formation?
When 1 mole of substance is formed from its constituent elements under standard conditions.
What is the standard enthalpy change of combustion?
When 1 mole of a substance undergoes complete combustion under standard conditions
What is the standard enthalpy change of neutralisation?
When solutions of an acid and alkali neutralise under standard conditions to produce 1 mole of water.
What is Hess’s Law?
Total enthalpy change for a reaction is independent of the route
Where do the arrows go in a formation enthalpy change?
Upwards (products - reactants), put the constituent elements at the bottom
Where do the arrows go in a combustion enthalpy change?
downwards (reactants - products), put the combustion products at the bottom
What is the energy change equation?
Q = M(g) x Cp(specific heat capacity) x Delta T(don’t matter)
What is a mean bond enthalpy?
Enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules
Where do the arrows go in a mean bond enthalpy change?
Downwards, gaseous atoms of elements go at bottom
How to make calorimetry more accurate?
Take temp at regular time intervals and extrapolate the line to find the time the products and reactants were added.
