C5 energy changes Flashcards
what is the conservation of energy rule
Energy is not created or destroyed, only transferred. The total amount of energy in the universe stays the same.
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 that transfers energy to the surroundings
name 2 features of exothermic reactions
Give two examples
-temperature of surroundings increases
-product molecules must have less energy than the reactants by the amount transferred
Combustion, neutralisation reaction.
what’s an endothermic reaction
a reaction that takes in energy from the surroundings so the temperature of the surroundings decreases
what are 2 features of an endothermic reaction
Give an example of a use of an endothermic reaction.
-temperature of surroundings decreases
-product molecules must have more energy than reactants
For example sports injury packs.
what is activation energy
minimum amount of energy that particles that need to have to react
Difference in energy between the energy of the reactants and the highest point in the reaction profile.
why must energy be supplied in reactions
to break down the bonds of the reactants
how do you calculate overall energy change
sum of energy taken in to break bonds - sum of energy released to form bonds
what are cells
they contain chemicals which react to produce electricity
how can a simple cell be made
connecting two different metals in contact with an electrolyte
what is a battery
two or more cells together to grant a greater voltage
explain non rechargeable batteries
-chemical reactions stop when one of the reactants has been used up
-alkaline batteries are always non-rechargeable
explain rechargeable batteries
chemical reactions are reversed when an external electrical current is supplied
what are some advantages of hydrogen fuel cells
what about disadvantages?
Advantages:
-can be used constantly provided fuel is supplied.
-only produces water when burnt (no greenhouse gas emissions)
Disadvantages:
-hydrogen gas needs to be stored at high pressure and is difficult to transport
What are some advantages of rechargeable cells/batteries?
What about disadvantages?
Advantages:
-Can be recharged using electricity so fuel does not have to be supplied.
Disadvantages:
-Hard to dispose of (non-biodegradeable)
-Will eventually stop working