Section 4 - Pgs 59-63 Flashcards
Does breaking bonds require energy to be supplied or is energy released?
Energy has to be supplied to break bonds. (ENDOTHERMIC)
Does forming bonds require energy to be supplied or is energy released?
Energy is released when new bonds are formed. (EXOTHERMIC)
What is an exothermic reaction?
One which gives out energy to the surroundings, usually in the form of heat.
How can an exothermic reaction be detected?
By a rise in temperature (of the surroundings).
What causes an exothermic reaction to be exothermic?
The energy released in bond formation is greater than the energy required to break the original bonds.
What is an endothermic reaction?
One which takes in energy from the surroundings, usually in the form of heat.
How can an endothermic reaction be detected?
By a fall in temperature (of the surroundings).
What causes an endothermic reaction to be endothermic?
The energy required to break the original bonds is greater than the energy released in bond formation.
What is enthalpy change?
The overall change in energy in a reaction (per mole).
What is the symbol for enthalpy change?
ΔH
What is the unit for enthalpy change (ΔH)?
kJ/mol (Kilojoules per mole of the reactant)
When is enthalpy change (ΔH) positive and why?
When the reaction is endothermic - because the reaction takes IN energy.
When is enthalpy change (ΔH) negative and why?
When the reaction is exothermic - because the reaction is giving energy OUT.
What is an energy level diagram?
A diagram used to show how the energy in a reaction changes as the reaction progresses.
What is on the x and y axis of an energy level diagram?
x axis - Progress of reaction
y axis - Energy
What does the height from the reactants to the top of the curve represent on an energy level diagram?
The activation energy.
What is activation energy?
The minimum energy required to break the original bonds in the reactants (i.e. How much energy in needed for the reaction to happen).
In an exothermic energy level diagram, are the products higher or lower than the reactants and why?
Lower - because energy is given out from the reaction, reducing how much energy is in the reaction.
(Diagram pg 60)
In an endothermic energy level diagram, are the products higher or lower than the reactants and why?
Higher - because energy is taken in by the reaction, increasing how much energy is in the reaction.
(Diagram pg 60)
What does the height from the reactants to the products represent on an energy level diagram?
The enthalpy change.
What can lower the activation energy of a reaction?
A catalyst.
How does a catalyst work?
It provides an alternative pathway for the reaction with a lower activation energy.
How is a catalyst represented on an energy level diagram?
A lower curve which reaches the products line earlier.
Does a catalyst change the overall energy change for a reaction?
No, it remains the same.