Energy Changes Flashcards
AI (30 cards)
What is an exothermic reaction?
A chemical reaction that gives out heat to the surroundings.
What is an endothermic reaction?
A chemical reaction that takes in heat from the surroundings.
How does temperature change in an exothermic reaction?
The temperature of the surroundings increases.
How does temperature change in an endothermic reaction?
The temperature of the surroundings decreases.
Give an example of an exothermic reaction.
Combustion or neutralisation.
Give an example of an endothermic reaction.
Thermal decomposition or photosynthesis.
What does a reaction profile diagram show?
It shows the energy of reactants and products during a chemical reaction.
How does a reaction profile diagram look for an exothermic reaction?
The products are lower in energy than the reactants.
How does a reaction profile diagram look for an endothermic reaction?
The products are higher in energy than the reactants.
What is activation energy?
The minimum amount of energy needed for a reaction to occur.
Where is activation energy shown on a reaction profile?
It’s the energy barrier between the reactants and the peak of the curve.
Why is activation energy important?
It determines whether a reaction will start — particles must collide with enough energy.
What happens to bonds during a chemical reaction?
Bonds in the reactants break and new bonds in the products form.
Is bond breaking endothermic or exothermic?
Endothermic — it takes in energy.
Is bond making endothermic or exothermic?
Exothermic — it releases energy.
What determines if a reaction is overall exothermic or endothermic?
The balance between energy taken in for bond breaking and energy released during bond making.
What happens if more energy is released in bond making than taken in for bond breaking?
The reaction is exothermic.
What happens if more energy is taken in for bond breaking than released in bond making?
The reaction is endothermic.
How do you calculate energy change from bond energies?
Add total energy for bonds broken, subtract total energy for bonds formed.
What is the formula for energy change in a reaction?
Energy change = total energy in (bonds broken) – total energy out (bonds formed).
Why are bond energies average values?
Because bond strength varies slightly in different molecules.
How can bond energy calculations be used to predict reaction types?
If the result is negative, the reaction is exothermic; if positive, it’s endothermic.
Why do endothermic reactions feel cold?
They absorb heat energy from the surroundings.
Why do exothermic reactions feel hot?
They release heat energy to the surroundings.
