Energetics Flashcards
Enthalpy change definition
change in heat energy at a constant pressure
standard conditions for enthalpy changes
-1 atm pressure
-298K
-1.0 mol dm-3 conc
activation energy reaction
minimum energy needed to start a reaction
mean bond enthalpy definition
the energy required to break one mole of a covalent bond into gaseous atoms, averaged over a range of different compounds
acronym for Bond Enthalpy
BERP
equation for mean bond enthalpy
Reactant - Products
standard enthalpy of formation definition
-The enthalpy change when one mole of substance is formed
-from its constituent elements under standard conditions
-with all reactants and products being in their standard states.
standard enthalpy of combustion
-The enthalpy change when one mole of a substance
-is completely burnt in excess oxygen
-under standard conditions, all reactants and products being in their standard states
Give one reason why the bond enthalpy that you calculated above is different from the mean bond enthalpy quoted in a data book
The data book value is averaged over a range of different compounds
Calorimetry equation
Q=mc(change in T)
Q/1000
Q/n = enthalpy change
How to minimise sources of error in calorimetry
-add a lid
-insulate the sides
-reduce distance between flame and beaker
-put a sleeve around the flame
-continuously stir
steps to measure an enthalpy change using a
-Record the temperature for a suitable time (3 minutes) before adding reactants together
-To establish an accurate initial temperature
-Mix reactants then record temperature every minute until a trend is seen
-Plot a graph of temperature against time
-Extrapolate the cooling curve back to the point of addition
-To establish a theoretical temperature change accounting for heat loss
