9.1 Enthalpy Changes Flashcards
Define enthalpy
A measure of the heat energy in a chemical system
How do you work out enthalpy change?
Enthalpy of products - enthalpy of reactants
What is the difference between the surroundings and the system?
System : reactants and products
Surroundings : apparatus, the lab
Define exothermic and endothermic changes in terms of the system and its surroundings
Exothermic = energy transferred from system to surroundings
Endothermic = energy transferred from surroundings to the system
When is delta H negative and positive?
Negative = exothermic Positive = endothermic
What would the enthalpy profile diagram look like for an exothermic reaction?
Reactants higher than products
What would the enthalpy profile diagram look like for an endothermic reaction?
Reactants lower than products
Define activation energy
The energy input required to break bonds - the minimum energy required for a reaction to take place.
What are the axis for enthalpy profile diagrams?
y = enthalpy H x = progress of reaction
List the standard conditions
Pressure = 100 kPa Temperature = 298 K (25°C) Concentration = 1 mol dm-3 State = physical state in standard conditions
Define the 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.
Define the enthalpy change of formation
The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states
Define the enthalpy chance of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states
Define the enthalpy change of neutralisation
The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions with all reactants and products in their standard states.
