topic five: energy changes Flashcards
what happens in an exothermic reaction?
thermal energy is transferred from the chemicals to the surrounding. as there is more thermal energy, the temperature goes up
give on example of a use of an exothermic reaction
as a hand warmer or in self heating foods
what reactions are exothermic?
oxidation reactions, combustion reactions, and neutralization reactions
what happens in an endothermic reaction?
thermal energy is transferred from the surroundings to the chemicals. as there is less thermal energy there is a decrease in temperature
give an example of a use of an endothermic reaction
in cold packs
what reactions are endothermic?
decomposition reactions, and reactions of acids and metal hydro-carbonates
what is activation energy?
the minimum amount of energy that particles need in order to react
in the reaction profile of an endothermic reaction is the overall energy change positive or negative
positive as the chemicals are gaining thermal energy from their surroundings
in the reaction profile of an exothermic reaction is the overall energy change positive or negative
negative as the chemicals are losing thermal energy from their surroundings
draw and label a reaction profile for an endothermic reaction
energy on y-axis
progress of reaction on x-axis
reactants drawn to the left
products drawn to the right and above the reactants
curve drawn connecting reactants and products
activation energy and overall energy change labelled
draw and label a urreaction profile for an exothermic reaction
energy on y-axis
progress of reaction on x-axis
reactants drawn to the left
products drawn to the right and below the reactants
curve drawn connecting reactants and products
activation energy and overall energy change labelled
during a chemical reaction:
making bonds…
breaking bonds…
energy is released when bonds are made
energy must be supplied to break the bonds
what does the overall energy change equal
the difference between the energy needed to break the bonds and the energy needed to make the bonds
in an exothermic reaction…
(bond energies)
more energy is released than is needed to break the bonds so the overall energy change is negative
in an endothermic reaction…
(bond energies)
more energy is needed to break the bonds than is released when making them so the overall energy change is positive
