P1-Topic 5- Energy changes 2022 Flashcards
What is the conservation of
energy principle? 2
that energy is neither created nor destroyed
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? Give examples 3
reaction where energy is transferred to the surroundings so that the surroundings temperature increases
combustion, oxidation, neutralisation
Negative sign of energy change.
What is an endothermic
reaction? Give examples
3
A reaction where energy is taken in from the surroundings so the surroundings
temperature decreases
thermal decomposition, reaction of citric acid and sodium hydrogencarbonate.
positive sign of energy change.
What is activation energy?
Minimum amount of energy that particles need to react
What occurs in a chemical reaction in terms of bond energies?
2
exothermic – energy released from forming bonds is greater than that needed to break the bonds;
endothermic – energy needed to break bonds is greater than
energy released making them
What is the equation to find enthalpy (energy) change in terms of bond energies?
Energy of reaction = sum of bonds broken – sum of bonds made
reactants-products
What is a cell?
two electrodes dipped in an electrolyte solution.
Cells contain chemicals which react to produce electricity
What is a battery?
A battery consists of two or more cells connected in series
What determines the voltage obtained from a cell?
Identities of metals used as electrodes
identity and concentration of an
electrolyte.
State the advantages and disadvantages of using cells and batteries.2
+) more or less cheap, some are rechargeable, a convenient source of electrical energy
(-) harmful chemicals
Describe rechargeable and non-rechargeable cells 3
Rechargeable – chemical reactions are reversed when an external current is
supplied
Non-rechargeable – reactants are used up, cannot be recharged (alkaline)
What is a fuel cell?
Fuel cells are supplied by fuel and oxygen to oxidise the fuel to generate
electricity.
What is the overall reaction in a hydrogen fuel cell? What are the half equations?3
Cathode: 2 H₂ → 4 H+ + 4 e−
Anode: O₂ + 4 H+ + 4 e−→ 2H₂O
Overall: → 2 H₂+ O₂ → 2 H₂O
What are the advantages and
disadvantages of hydrogen
fuel cells?
Advantages: no pollutants, no recharging
Disadvantages: flammable, H2 difficult to store, fossil fuel production, toxic
chemicals, expensive production of H2
by electrolysis
which side are reactants and products on a reaction profile
reactants on the left and products on the right
