9.1- Enthalpy Changes Flashcards
What is enthalpy ?
Measure of the heat energy in a chemical system
What is the total chemical energy inside a substance called ?
Enthalpy
What is the symbol of enthalpy change ?
/_\ = change
H = enthalpy
/_\H
What is an exothermic reactions?
- A reaction is exothermic when the products have less energy than the reactants
- heat energy is given off by the reaction to the surroundings
- temp of the environment increases
- energy of the system decreases
- enthalpy change is negative
Can you measure enthalpy?
No but you can measure enthalpy change
Is there a enthalpy decrease or increase in an exothermic reaction?
Enthalpy decrease thus the /_\H is negative
What is a endothermic reactions?
- A reaction is endothermic when the products have more energy than the reactants
- heat energy is absorbed by the reaction from the surroundings
- temperature of the environment decreases
- energy of the system decreases
- enthalpy change is positive
Is there a enthalpy increase or decrease during an endothermic reaction?
Increase
/_\H is positive
What process is required to break forces of attraction - bond breaking?
Endothermic
What are the system , surroundings and universe ?
System = chemicals- reactants and products
Surroundings = are the apparatus eg. Thermometer , the laboratory and everything that’s not the chemical system
Universe = is everything and includes both system and surroundings
What two directions can energy transfer be in ?
From the system to the surroundings - exothermic
From the surroundings to the system- exothermic
Define enthalpy changes
The bond (dissociation) enthalpy is the energy needed to break one mole of the bond to give separated atoms - everything being in the gas state
