topic 4 energy changes Flashcards
What is the conservation of energy principle?
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.
What is an exothermic reaction?
I reaction where allergies is transferred to the surroundings so that surrounding temperature increases – combustion, oxidation reactions and neutralisation reactions
What is an endothermic reaction?
A reaction where energies is taken in from the surrounding so the surrounding temperature decreases – thermal decomposition, reaction of citric acid and sodium hydrogen carbonate
what is activation energy?
Minimum amount of energy that particles need to react
What is a reaction profile?
Reaction profile is a graph which shows relative energies of reactants and product as well as activation energy of reaction
what occurs in a chemical reaction in terms of bond energies? Describe exothermic and endothermic reactions in terms of bond breaking/forming
Energy is supplied to break bonds and energy release when bonds are made; exothermic – energy release from forming bonds is greater than needed to break the bonds; endothermic – energy needed to break bonds is greater than energy release making them
what is the equation to find
enthalpy change in terms of bond energy?
Energy of reaction=sum of bonds broken - sum of bonds made
what is a cell?
A cell is composed of two electrons dipped in an electrolyte solution.
It produces electricity from a chemical reaction
what is the battery?
A battery consist of two or more cells connected in series
What determines the voltage obtained from a cell?
identities of metal used as electrodes and the identity of concentration of electrolyte
State the advantages and disadvantages of using cells and batteries
more or less cheap, some are rechargeable, a convenient source of electrical energy
Harmful chemicals
describe rechargeable and non-rechargeable cells
Rechargeable – chemical reactions are reverse when an external current is supplied
Non-rechargeable – reactants are used, cannot be recharged
What is a fuel cell?
Fuel cells are supplied by fuel and oxygen to oxidise the fuel to generate electricity
what are the advantages and disadvantages of hydrogen fuel cells?
Advantages: no pollutants, no recharging
Disadvantages: flammable, H2 difficult to start, fossil fuel production, toxic chemicals, expensive production of H2 by electrolysis
