Energetics Flashcards
bond breaking is (exothermic/endothermic)
endothermic
bond forming is (exothermic/endothermic)
exothermic
Endothermic reactions (release/absorb) energy
absorb
Exothermic reactions (release/absorb) energy
release
Endothermic reactions are (cold/hot)
cold
Exothermic reactions are (cold/hot)
hot
Endothermic reactions have a (positive/negative) delta H
positive
Exothermic reactions have a (positive/negative) delta H
negative
Temperature
average kinetic energy of a substance
Heat
the total kinetic energy of a substance
Units of heat
Joules (J) or kilojoules (kJ)
Specific heat capacity
the joules of heat that are needed to raise the temperature of one gram of a substance by one Kelvin
units of specific heat capacity
J/g/K
q/delta H/energy change =
mc delta T M = mass of the substance being heated C = SHC Delta T = temperature change Unit of q is J
SHC calculations could be inaccurate due to:
Lack of insulation
Heating the container/vessel
Ways to improve accuracy of SHC calculation:
Insulate calorimeter
Use a lid on the calorimeter
Which reactions have a negative enthalpy change (negative delta H)?
neutralisation, combustion
Standard enthalpy change of formation
energy change when 1 mole of a substance is formed from its elements in their standard state
Standard state
pure form of the substance at STP
Standard enthalpy change of combustion
energy change when 1 mole of a substance is burnt at STP
Enthalpy of formation of oxygen
zero
Enthalpy change of a reaction =
enthalpy of formation of the products - enthalpy of formation of the reactants
Lower energy means (more/less) stable
more
Average bond enthalpy
the energy needed to break one mol of a bond in a gaseous molecule averaged over similar compounds
Average bond enthalpy calculations
find the enthalpy for each compound, ones on the left are positive, ones on the right are negative, then sum up
Why are ozone bonds easier to break than oxygen bonds?
Ozone has a resonance structure, so the bonds average out to 1.5, which makes it easier to break than O2, which has a double bond
