Enthalpy Changes Flashcards
What is enthalpy?
A measure of the heat energy stored in a chemical system
What are standard conditions?
Gases at 100kPa
298K temperature
Solutions 1.00moldm-3
All substances in their standard physical states
Standard enthalpy change of reaction
Enthalpy change accompanying a reaction in the molar quantities shown in the chemical equation, under standard conditions and with all reactants and products in their standard states
Standard enthalpy change of formation
Enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
Standard enthalpy change of combustion
Enthalpy change when one mole of a compound is completely burnt in oxygen under standard conditions
Standard enthalpy change of neutralisation
The enthalpy change accompanying the reaction of an acid with a base to form one mole of water, under standard conditions, with all reactants and products in their standard states
What is the major source of error in enthalpy change of reaction calculations and how can this error be reduced?
Heat loss to surroundings
Add lid to polystyrene cup
Add insulation around polystyrene cup
What is activation energy?
The minimum energy required for a reaction to take place
What is average bond enthalpy?
The mean amount of energy required to break one mole of a specified type of covalent bond in gaseous molecules
What does Hess’s law state?
That if a reaction can take place by more than one route, and the starting and finishing conditions are the same, the total enthalpy change is the same for each route
Why does increasing concentration increase rate of reaction?
More particles per unit volume so particles are closer together and collisions are more frequent. Rate increases
What is a catalyst and what does it do?
A catalyst increases the rate of reaction without being used up over the whole reaction. It provides an alternative reaction pathway with a lower activation energy
What is la Chatelier’s principle?
When a system in dynamic equilibrium is subjected to a change in conditions, the position of equilibrium shifts to minimise the change
