1.4 Energetics Flashcards
State an exothermic and endothermic process
Exothermic : energy released from chemical to surroundings during the process, temperature of surroundings increases
Endothermic : energy taken by chemical from surroundings during process, temperature of surroundings decreases
Exo : negative delta H
Endo : opposite
Define enthalpy change
Change in heat energy at a constant pressure
What are the standard conditions
100kPa
298 K
1.0 mol dm^3 concentrations for all solutions
State of a chemical is solid, liquid or gas
Draw an enthalpy level diagram for exothermic and endothermic reactions
Define mean bond enthalpy
Energy required to break one mole of a covalent bond into gaseous atoms, averaged over a range of different compounds
a) State why enthalpy of formation of Na(s) is zero
b) state why enthalpy of formation of Na(l) is not zero
a) Na is an element
b) Na is not in it’s standard state
Define standard enthalpy of combustion
The enthalpy change when one mole of a substance
Is completely burnt in oxygen
Under standard conditions, all reactants and products being in their standard states
Why may enthalpy of combustion be difficult to measure
Incomplete combustion may occur
Why is bond enthalpy you calculated different from mean bond enthalpy quoted in data Booklet
Data book value is averaged over a range of different compounds
How to use the three Hess cycles
Two equations needed for calorimetry
Q= mc x delta t
Delta H = Q/n
n = moles
Delta H = enthalpy change
Equipment needed for combustion
Assumption made in calorimetry
Errors with combustion and solution calorimetry, state fixes
How to measure an enthalpy change using a cooling curve
Define standard enthalpy of formation
Enthalpy change when one mole of a compound if formed from it’s elements under standard conditions, all reactants and products being in their standard states
Method for caoliromtetry
- mass = 50 grams because density is 1 g cm^-3 , so if you multiply it by volume of zinc, you get mass of 50 grams
- final answer has a negative sign because temperature increases, if temperature decreases, then you use a positive sign
Equation for mark 1 is KCLO4 -> KCl + 2O2
