Energetics Flashcards
what is the standard condition of pressure
100kpa
what is the standard condition of temperature
298K
symbol to show standard conditions have been used
Ꝋ
standard enthalpy change of reaction definition
endo or exo
The enthalpy change when the reactants in the equation react to give the products under standard conditions
both
standard enthalpy change of formation definition
endo or exo
the enthalpy change when one mole of a compound is formed from its elements under standard conditions
both
standard enthalpy change of combustion definition
endo or exo
the enthalpy change when one mole of a substanbce is burnt under excess oxygen under standard conditions
exo
standard enthalpy change of neutralisation definition
endo or exo
the enthalpy change when one mole of water is formed by reacting an acid and alkali under standard conditions
exo
exothermic
energy is released to the surroundings
- sign
endothermic
energy is absorved from the surroundings
+sign
enthalpy definition
total chemical energy inside a substance
ΔH = enthalpy change
things needed in an energy level diagram
reactants first line
arrow going up or down with ΔH
final line of products
Y = energy kj/mol
X= extent of reaction
calorimetery definition
the measurement of enthalpy changes in chemical reactions
simple calorimeter how to make
polystyrene cup
thermometer
water
SHC defintion
energy required to raise the temperature of 1g of a substance by 1 degree celsius
how to calculate enthalpy change
q=mc ΔT
divide 1000
divide moles of thing you are calculating the enthalpy of
what does hess law state
the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same
equations to be used in hess law calculations
ΔHr = ΔH2 – ΔH1
what type of process is breaking a bond
endothermic as it requires the input of energy
what is the bond dissocation enthalpy
the energy required to break a particular bond
what type of proccess is forming a bond
exothermic as energy is released
what is the amount of energy required when a particular bond is broken the same as
the amount of energy released when forming a bond
what does it mean if more energy is required to break bonds than is relaeased in the forming of bonds
the overall reaction is endothermic
products are less stable than the reactants +
what does it mean if less energy is required to break bonds than is relaeased in the forming of bonds
exothermic overall reaction
products are more stable than the reactants
what is the average bond energy
the energy needed to break one mole of bonds in a gaseous molecule averaged over similar compounds.
why is the first c-H bond easier to break than the second
the remaining hydrogens are pulled more closely to the carbon
why do we need an average bond enthalpy
it is impossible to measure the energy of each C-H bond
so we compare the value with simialr compounds,
why are bond energies used to calculare ΔHrꝋ
when we cannot do it experimentally
ΔHrꝋ equation
ΔHrꝋ = enthalpy change for bonds broken + enthalpy change for bonds formed
