energy changes Flashcards
what is an exothermic reaction?
a reaction in which heat energy is given off- more energy is released when new bonds are formed than energy required to break the bonds in the reactants. has a negative enthalpy value.
what is an endothermic reaction?
a reaction in which heat energy is taken in from the surroundings- more energy is needed to break bonds than is released in making bonds. has a positive enthalpy value
enthalpy change (ΔH) = …?
energy taken in - energy given out
what are some uses of endo and exothermic reactions?
endothermic- sports injury packs
exothermic- self heating food, hand warmers
what are some examples of exothermic reactions?
combustion, neutralisation, oxidation, displacement
what are some examples of endothermic reactions?
therman decomposition, alkane cracking, sodium hydrogencarbonate + citric acid
what is the link between reactivity and energy changes?
the bigger the difference in reactivity in a displacement reaction, the more exothermic the reaction
what is activation energy?
the minimum amount of energy required to start a chemical reaction.
describe an energy profile diagram for an exothermic reaction
reactants are at a higher energy level than products
describe an energy profile diagram for an endothermic reaction
products are at a higher energy level than reactants.
what is the definition of bond energy?
the average amount of energy that will break/make a bond between two atoms
what is a catalyst + how do they work?
a substance that speeds up the rate of a chemical reaction without being used up- provides an alternate reaction pathway with lower activation energy
what is an electrochemical cell?
a device containing chemicals that react to produce electricity- 2 or more cells together in series form a battery
what factors determine a cell’s voltage?
type of electrode, concentration of electrolyte, type of electrolyte
how are some cells rechargeable?
the chemical reaction is reversed when a current is applied
