3.2 Flashcards
Enthalpy change of REACTION
The energy change associated with a given reaction
Enthalpy change of FORMATION
The energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard state under standard conditions
Enthalpy change of COMBUSTION
The energy change that takes place when 1 mole of a substance is completely combusted
Enthalpy change of NEUTRALISATION
The energy change associated with the formation of 1 mole of water from a neutralisation reaction
Standard conditions ⦵
298K and 100kPa
AVERAGE bond enthalpy
The enthalpy change for breaking 1 mole of bonds in gaseous molecules
Calorimetry
The quantitative study of energy in a chemical reaction
Specific heat capacity
The energy required to raise the temperature of 1g of a substance by 1K
Equation to find heat exchanged in a reaction
q = mc△T
Hess’ Law
The enthalpy change in a chemical reaction is independent of the route it takes
Dynamic equilibrium
Where the rate of reaction is the same in both directions, meaning concentrations of products and reactants don’t change
Le Chatelier’s Principle
If equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change
I.C.E
Initial moles
Change of each
Equilibrium moles, concentrations
Activation energy
The minimum energy that particles need for collisions to be successful and result in reaction
Significance of equilibrium constants
K = 1 = middle
K < 1 = favours backward reaction
K > 1 = favours forward reaction
What is the effect of increasing T on a Boltzmann Distribution?
Shifts peak to the right, lowers peak, but area under curve stays approximately the same
Which moles do you use when measuring △H in q/mol?
Moles of limiting reactant (not in excess) for reactions in a solution OR moles of fuel for combustion reactions (spirit burner)
Homogeneous catalyst
Same phase as reactants
Heterogeneous catalyst
Different phase to reactants (could be immiscible liquid)
3 stages of heterogeneous catalysts
ADSORPTION (to active site of catalyst)
REACTION (rearrangement of electrons)
DESORPTION (products released)
Enthalpy equation
△H = q / moles
- q must be in kJ
How do you calculate △H?
△H = H(products) - H(reactants)
Why is average bond enthalpy less accurate than direct measured values / other enthalpy values?
It is a mean value for the bond enthalpy in a variety of environments in different molecules
