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Sciene Chem > energy changes 5 > Flashcards

energy changes 5 Flashcards

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1
Q

what happens to energy in a reaction

A

energy is conserved in reactions and only move around

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2
Q

what is an exothermic reaction

A

one that transfers energy to the surroundings usually by heating

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3
Q

examples of exothermic reactions

A

combustion
neutralisation reactions
oxidation reactions

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4
Q

what is an endothermic reaction

A

one that takes in energy from the surroundings

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5
Q

examples of endothermic reactions

A

thermal decomposition

reaction between citric acid and sodium hydrogencarbonate

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6
Q

everyday uses of endothermic reactions

A

sports injury packs (allow the pack to become instantly cooler)

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7
Q

everyday uses of exothermic reactions

A 
hand warmers(oxidation of iron in air to release energy)
self heating cans(chemicals in there base)
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8
Q

what happens to bonds during a reaction

A

old bonds break and new ones form

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9
Q

what reaction is bond breaking

A

endothermic

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10
Q

what reaction is bond forming

A

exothermic

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11
Q

what reaction has a minus in bond calculations

A

exothermic

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12
Q

what reaction has plus in bond calculations

A

endothermic

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13
Q

what are reaction profiles

A

diagrams that show the relative energies of the reactants and products in a reaction

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14
Q

what is the activation energy

A

the initial rise. and is the minimum amount of energy the reactants need to collide with each other and react.

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15
Q

what does the difference in height mean in reaction profiles

A

represents the overall energy change in the reaction

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16
Q

what is at higher energy by the end of an exothermic reaction. Product or reactant

A

reactants

17
Q

what is at higher energy by the end of an endothermic reaction. Product or reactant

A

products

18
Q

what is an eletrochemical cell

A

a basic system made up of two different electrodes in contact with an electrolyte
two electrodes are usually metal

19
Q

what is electrolyte

A

a liquid that contains ions that react with the electrodes

20
Q

how cells produce energy

A

chemical reaction between the electrodes and the electrolyte set up a charge difference between the electrodes.
If the electrodes are then connected by a wire, the charge is able to flow and produces electricity.

21
Q

what factors change the voltage of a cell

A

type of electrodes

electrolyte

22
Q

what happens in a normal cell

A

chemical reaction at the electrode are irreversible

the ions in the electrlyte and the metal ions on the electrode get used up

23
Q

what happens in a re chargeable cell

A

reaction can be reversed by connecting it to an external electric current

24
Q

how is a battery formed

A

connecting two or more cells together in series

25
Q

disadvantages of using hydrogen fuel cells

A

Takes up lots of space
explosive so hard to store
hydrogen made from hydrocarbons which mean they still pollute

26
Q

advantages of using hydrogen fuel cells

A

don’t produce as many pollutants
batteries are more expensive
batteries store less energy so need charging
batteries need replacing

27
Q

why batteries are better than conventional fuels

A

conventional fuels have finite supply

batteries and fuel cells are cleaner

28
Q

what is a fuel cell

A

is an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy sufficiently

29
Q

how do fuel cell work

A

fuel enters the cell it becomes oxidised and sets up a potential difference within the cell

30
Q

how hydrogen oxygen fuel cell works

A

Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment

at the anode hydrogen loses electrons to produce H plus ions

H plus ions in the electrolyte move to the cathode

at the cathode oxygen gains electrons from the cathode and reacts with H plus ions to make water

the electrons flow through an external circuit from anode to cathode

overall reaction is hydrogen + oxygen = water

Sciene Chem (14 decks)

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