Enthalpy changes Flashcards
What is enthalpy?
A measure of heat in a chemical system
Why do most chemical reactions have an enthalpy change?
Reactants and products have different bonds and structures so different amounts of energy
What’s a system?
The reactants and products
What’s the surroundings?
The rest of the universe
What is a chemical reaction that is exothermic?
Energy transferred from the system to the surroundings, ΔH is negative
What is a chemical reaction that is endothermic?
Energy transferred from the surroundings to the system, ΔH is positive
How to draw enthalpy level diagram for exothermic reaction?
Enthaply on y axis
Progress of reaction on x axis
Reactants higher than products
ΔH is the difference between the 2 lines
The activation energy is the distance from the reactants to the peak of the curve
How to draw enthalpy level diagram for exothermic reaction?
Enthaply on y axis
Progress of reaction on x axis
Reactants lower than products
ΔH is the difference between the 2 lines
The activation energy is the distance from the reactants to the peak of the curve
Activation energy definition?
The minimum energy required to start a reaction by the breaking of bonds
Why do most chemical reactions have an activation energy?
It’s necessary to break bonds in the reactant molecules
Equation for heat energy change in a reaction?
q= m x c ΔT
What’s q?
Heat energy change for the reaction carried out, measured in Joules
What’s m?
Mass of material for which the temperature change is measured in (eg the amount of water in solution)
What’s c?
Heat capacity of material for which temp is measured in eg. in water of solution = 4.18
what is ΔT?
Temp change measured in kelvin or degrees
