c7 - energy changes

exothermic is what

energy transferred to the surroundings

endothermic is what

taking in energy from the surroundings

burning of fuel is what type of reaction

exothermic

neutralisation between acids and alkalis is what type of reaction

exothermic

how can you see neutralisation reaction between acid and alkali is exothermic

temperature rise

what type of reaction is more common: endothermic or exothermic

exothermic

examples of endothermic reactions

decomposition of calcium carbonate

handwarmers use what type of reaction

exothermic

what do chemical cold packs contain

wtaer and ammonium nitrate

unit from relative amount of energy contained in the reactants and the products in a reaction profile

kilojoules per mole

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what is the activation energy

the minimum amount of energy the reactants need to cause a reaction

bond breaking is what

endothermic

bond making is what

exothermic

bond energy is what

the energy needed to break the bond between two atoms in called the bond energy for that bond

what are bond energies measured in

kj/mol

what do electrical cells and batteries rely on

differing reactivity of metals

how can you use difference in reactivity in metals to make an electrical cell or battery

• join them by a wire 
  - dip in electrolyte solution
  - electrons flow through wire from zinc to copper

voltage and reactivity rule

the greater the difference in reactivity between the two metals used, the higher the voltage produced

how do metals tend to react

lose electrons and form positive ions

what is an alternative to fossil fuel that is a gas

hydrogen

waste product of hydrogen fuel cells

water

how is fuel in fuel cells oxidised

electrochemically within the fuel cell

why is the fuel in fuel cells oxidised

to make a potential difference

oxidation of hydrogen = what

water

half equation in a fuel cell anode

2H₂🡢​ 4H⁺+4e^-

half equation in a fuel cell cathode

O₂+4H⁺+4e^- 🡢 2H₂O

overall reaction in a hydrogen fuel cell

2H₂+O₂ 🡢 2H₂O

oxidation

loss of electrons

reduction

gain of electrons