energy changes Flashcards
exothermic
releases energy to surroundings increasing temperature around
example of exothermic reactions
- combustion
- any oxidation reactions
- neutralisation
everyday uses of exothermic reactions
- self-heating cans
- hand warmers
endothermic
takes in energy from surroundings, decreasing temperature around
example of endothermic reactions
- thermal decomposition
- reactionn of citric acid and sodium hydrocarbonate
everydy use of endothermic reactions
sports injury packs
bond breaking
endothermic
(+) change in energy
bond making
exothermic
(-) change in energy
energy change=
endo-exo
energy taken in - energy given out
what is an electrolyte?
solution that can conduct electricity
what is a cell
2 different metals connected together and in contact with an electrolyte
produces potential difference
what does the potential difference created by cells dependent on
- reactivity between the two metals
- ^ reactivity ^pd
- electrolyte
what is a battery and why is it better than a cell?
- 2 or more cells connected in series circuit
- produces greater voltage
- also lasts longer as in a cell, the chemicals run out quickly
alkaline battery
- non-rechargeable
- reaction will run out
rechargebale batteries
can reverse reaction when electrical current applied
what happens in a fuel cell?
a fuel- hydrogen- is oxidised to produce potential difference
what happens in a hydrogen fuel cels
oxidation of hydrogen to produce water
they offer a potential alternative to rechargeable cells
anode
balanced half equation
2H2 -> 4H+ + 4E-
cathode
balanced half equation
O2 + 4H+ + 4E- -> 2H20
advantages of hydrogen fuel cells over rechargable cells
- dont produce pollution
- doesnt get less efficient
- continuous process- produce energy as long as H is supplied
disadvantages of hydrogen fuel cells over rechargable cells
- hydrogen is explosive
- ^ expensive to produce
- affected by low temperatures
