C7.1-4 - Energy Changes Flashcards
What is the Law of the Conservation of Energy?
Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place. If a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants, by the amount transferred.
What is an Exothermic reaction?
A reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases.
What is an Endothermic reaction?
A reaction is one that takes in energy from the surroundings so the temperature of the surroundings decreases.
What are some examples of Exothermic reactions?
Exothermic reactions include respiration, combustion, many oxidation reactions and neutralisation.
What are some examples of Endothermic reactions?
Endothermic reactions include photosynthesis, thermal decompositions and the reaction of citric acid and sodium hydrogencarbonate.
What is Activation energy?
Activation energy is the amount of energy (heat) need to start the (exothermic or endothermic) reaction.
Describe bond breaking in the reactants as an endothermic process?
Energy transfered from the surroundings to break bonds to overcome attraction between atoms
Describe bond formation in the products as an exothermic process?
New bonds in products STRONGER then old bonds in reactants.
How do you calculate the energy change in chemical reactions using bond energies supplied?
Bonds Brocken - Bonds Made = negative Exothermic, positive Exothermic.
How do you represent exo and endothermic reactions with reaction profiles (graphs)?
Endothermic reaction profile is when the graph goes upwards.
Exothermic reaction profile is when the graph goes down.
Which reaction is bond-breaking and which reaction is bond-making?
In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
What are some everday uses of exothemic reactions?
Everyday uses of exothermic reactions include self-heating cans and hand warmers.
What are some everday uses of endothemic reactions?
Some sports injury packs are based on endothermic reactions.
