chapter 4- energetics Flashcards
(19 cards)
what is the law of conservation of energy (first law)
energy can neither be created nor destroyed but it can be converted from one form to another
what happens to energy in exothermic reactions
energy is given out
what happens to energy in exothermic reactions
energy is given out
no to energy in endothermic reactions
energy in absorbed
what is enthalpy
a measure of the heat content of a substance at constant pressure
what are the standard conditions
pressure = 100KPa (1 atm)
Temperature= usually 298K (25degrees celsius)
conc of solutions= 1mol dm-3
what is enthalpy of formation
the enthalpy change when one mole of a compound is formed in its standard state from its elements in their standard states
what is standard enthalpy of combustion
the enthalpy change when one mole of a substance undergoes complete combustion under standard conditions. all reactants and products are in their standard states
is the standard enthalpy of combustion exothermic or endothermic
exothermic
what is enthalpy of neutralisation
the enthalpy change when one mole of water is formed from its ions in dilute solution
is enthalpy of neutralisation endothermic or exothermic
exothermic
what value is obtained when strong acids react with strong alkalis
- 57 KJ mol -1
what us bond disassociation enthalpy
the energy required to break one mole of gaseous bonds to form gaseous atoms
is bond disassociation enthalpy endothermic or exothermic
endothermic
what is Hess’s law
the enthalpy change is independent of the path taken
how is the overall enthalpy of reaction from bond enthalpies calculated
Σ bond enthalpies of reaction - Σ bond enthalpies of products
how is the overall bond enthalpy of reaction from enthalpies of formation calculated
Σ △Hf of products - △Hf of reactants
how do you calculate the overall enthalpy of reaction from enthalpies of combustion
Σ △Hc of reactants - Σ △Hc of products
what calculation is used to measure enthalpy change
q= m x c x △T
q= heat energy
m= mass
c= specific heat capacity
△T = change in temp
