Enthalpy Flashcards
What is the enthalpy change formation?
The enthalpy change is when ONE MOLE of a compound is formed from its elements in its natural state.
What is the enthalpy change combustion?
When ONE MOLE of a substance undergoes complete combustion
What is the enthalpy of neutralisation?
When ONE MOLE of water is formed from its ions in dilute solution
Enthalpy of solution?
When ONE MOLE of a substance is dissolved in water
Bond enthalpy?
Energy released making bonds > energy used to break bonds = Exothermic. Energy used to break bond > energy released making bonds Endothermic
How would you calculate enthalpy of solution?
Eh=mc(delta)T
= calculate 1mol x Eh
How would you calculate enthalpy of neutralisation?
Add volumes of reactants together
=) Eh=mcDT
= calculate 1mol x Eh
Calculate bond enthalpy
DH1=DH2-DH3 (Hess’s law)
What does Hess’ Law state?
If the starting and finishing points in a series of chemical reactions are identical, in the same state and with the same number of moles, then the change in enthalpy will be the same no matter which chemical route is taken
What are changes to the position of equilibrium known as?
Le Chatelier’s principle
How does concentration affect the position of equilibrium?
Increase in reactants/decrease in products = shifts right
Increase in products/decrease in reactants = shifts left
Describe what will happen to the position of equilibrium when pressure is changed
Increase in reactants/decrease in products = shifts right
Increase in products/decrease in reactants = shifts left
(remember equilibrium will shift to the side with fewer molecules - counteract change - so if same no. of molecules on both sides then no change)
Describe what will happen to the position of equilibrium when temperature is changed
Increase in temp = exothermic - left, endothermic - right
Decrease in temp = exothermic - right, endothermic - left
How does a catalyst affect the position of equilibrium?
It doesn’t, it will only increase the rate at which the reaction will reach dynamic equilibrium
When is a reversible reaction said to be at equilibrium?
When the rate of the forward reaction equals the rate of the reverse reaction
