Chapter 9 - Enthalpy Flashcards
Module 3
What is Enthalpy H?
Measure of heat energy in a chemical system.
What does a chemical system refer to?
The atoms, molecules, or ions making up the chemicals.
How to calculate the enthalpy change?
△H = H(products) - H(reactants).
What is the law of conservation of energy?
Energy cannot be created or destroyed it can only be transferred. During a chemical reaction involving enthalpy change the heat energy is transferred between the system and the surroundings.
How many directions can energy transfer occur?
In two directions.
Explain the directions for energy transfer?
From the system to the surroundings - exothermic change.
From the surroundings to the system - endothermic change.
Enthalpy profile diagram points for an exothermic reaction.
◈ The chemical system releases heat energy to the surroundings.
◈ An energy loss by the chemical system is balanced by the same energy gain by the surroundings.
◈ △H = negative.
◈ Temperature of the surroundings increases as they gain energy.
Enthalpy profile diagram points for an endothermic reaction.
◈ The chemical system takes in heat from the surroundings.
◈ Any energy gain by the chemical system is balanced by the energy loss by the surroundings.
◈ △H = positive.
◈ Temperature of the surroundings decreases as they lose energy.
What is activation energy?
It is the minimum amount of energy required for a reaction to occur.
