Module 3 - Enthalpy Change/ Equilibrium Flashcards
A closed system is required for dynamic equilibrium to be established
State one other feature of this dynamic equilibrium
Rate of the forward reaction is equal to the rate of the backward reaction
Concentration does not change
State le chatelier’s principle
The position of a dynamic equilibrium shifts to minimise the effect of any change
What is meant by the term standard enthalpy change of formation
Give the standard conditions
Standard enthalpy change of formation is the amount of energy needed for one mole of compound to form from its elements
25 degrees, 101 kPa
What is meant by the term average bond enthalpy?
When one mole of gaseous covalent bond is broken
Apart from heat loss, suggest two reasons for the difference in value from the data book.
Assume the calculation has been carried out correctly
Standard conditions are unlikely to be identical
Incomplete combustion can occur
What is enthalpy change of neutralisation
When one mole of water is formed
Why do Br2 and I2 not exist in gaseous state under standard conditions
Energy is needed to break London forces between molecules
Enthalpy change of vaporisation is the energy change when one mole of a substance changes from a liquid to a gas at its boiling point.
Suggest whether the enthalpy change of vaporisation of bromine is exothermic or endothermic.
Explain your answer
Endothermic because energy is required to overcome London Forces
Explain in terms of bond breaking and bond forming why a reaction can be exothermic
More energy is released by forming bonds than energy required when breaking bonds
Define standard enthalpy change of combustion.
Include the standard conditions that are used.
Standard enthalpy change of combustion is when one mole of a substance combusts fully with oxygen
25 degrees and 101kPa
Explain how a catalyst increases the rate of a chemical reaction
Catalyst lowers the activation energy
so there are greater proportion of molecules with energy greater than activation energy
