chapter 9 Flashcards
enthalpy
a measure of the heat energy in a chemical system
enthalpy change =
products- reactants
exothermic
releases heat energy to the surroundings
negative
endothermic
takes in heat energy from the surroundings positive
activation energy
the minimum energy required for a reaction to take place
standard conditions
100 kPa
298 K
1 mol dm-3
standard enthalpy change of reaction
the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation, under standard conditions, with all reactants and products in their standard states
standard enthalpy change of formation
the enthalpy change that takes place when one mole of compound is formed from its elements under standard conditions, with all reactants and products in their standard states
standard enthalpy change of combustion
the enthalpy change that takes place when one mole of substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states
standard enthalpy change of neutralisation
the energy change that accompanies the reaction of an acid by a base to form one mole of water under standard conditions, with all reactants and products in their standard states
calculating an energy change
q= mcDT
m=mass of the material changing temperature
c
4.18 Jg-1K-1
possible reasons why experimental values differ from data book values
- heat loss to the surroundings
-incomplete combustion (soot)
-evaporation of the alcohol
-non-standard conditions
first 3 lead to less exothermic results
average bond enthalpy
the energy required to break one mole of a specific bond in a gaseous molecule
bond breaking and bond making
- energy is required to break bonds- endothermic
- energy is released from bond making- exothermic
