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chemistry one > energy changes > Flashcards

energy changes Flashcards

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1
Q

what is an exothermic reaction

A

one that transfers energy to the surroundings so the temperature of the surroundings increase

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2
Q

what is an endothermic reaction

A

one that takes in energy from the surroundings so the temperature of the surroundings decreases

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3
Q

what is an example of an exothermic reaction

A

combustion, oxidation reactions

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4
Q

what is an example of an endothermic reaction

A

thermal decomposition

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5
Q

what is activation energy

A

the minimal amount of energy required for a chemical reaction to occur

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6
Q

draw an energy profile for an exothermic reaction

A

energy y axis
time of reaction x axis
reactions start high products end low
activation energy first half
energy release second half

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7
Q

draw an energy profile for an endothermic reaction

A

energy y axis
time of reaction x axis
reactants start low products end high
activation energy all the way down
energy absorbed between products and reactants

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8
Q

what do you need to break chemical bonds and what type of reaction does this mak, what sign do you need

A

need energy
creates an endothermic reaction
positive sign because energy is added to reaction

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9
Q

what happens when chemical bonds are made and what type of reaction is this, what sign is needed

A

energy is released
creates an exothermic reaction
negative sign because energy leaves the reaction

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10
Q

what is a bond value

A

the amount of energy required to break bonds

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11
Q

complete 2 bond energy practice questions

A

did you get them right??

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12
Q

What is an electrolyte

A

solution that can conduct electricity

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13
Q

what do the chemicals in cells do

A

react to produce electricity

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14
Q

what is the voltage produced by a cell dependent on

A

type of electrolyte

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15
Q

what is a battery

A

two or more cells connected to provide greater voltage

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16
Q

what are non rechargeable batteries made with and why do these batteries stop working

A

alkaline batteries
- when chemical reactions stop working, one of the reactants had been used up

17
Q

why are rechargeable batteries reusable

A

they can be recharged we can reverse the chemical reactions when we apply an electrical current

18
Q

what are fuel cells

A

a type of electrochemical cell

(converts energy between electric and chemical forms)

19
Q

what are the most common type of fuel cells

A

hydrogen - oxygen

20
Q

what do fuel cells make and what byproduct do fuel cells make

A

generates a lot of electrical energy
water

21
Q

draw a simple version of a fuel cell

A

cathode on right
anode on left
electrolyte in between
inlet on left for hydrogen
inlet on right for oxygen
outlet on right for water

22
Q

explain the process of fuel cells with hydrogen and oxygen

A
  1. hydrogen enters and is oxidised to become a hydrogen ion (because it looses its electron). this then creates a potential difference between the anode and cathode
  2. electrons pass through the wire to the cathode and the hydrogen passes through the electrolyte to the cathode. these all react with oxygen to create water and a hydrogen atom. this process needs to happen again in order to have an even number of waters.
23
Q

what is a half equation

A

shows the loss or gain of electrons

24
Q

what is the two equations for hydrogen - oxygen fuel cells

A

oxidation of hydrogen
H2 —– 2H+ + 2e-

reduction of oxygen
O2 + 4H2 +4e- ———- 2H2O

25
Q

what is the overall equation for hydrogen - oxygen fuel cells

A

O2+2H2 —– 2H20

26
Q

compare hydrogen fuel cells and rechargeable cells and batteries

A
  • fuel cells can be used constantly providing fuel is added in
  • hydrogen is a gas so it needs to be stored at high pressure - harder to transport
  • only produces water when burnt
  • fuel doesn’t need to keep being supplied
  • hard to dispose of - non biodegradable
  • will eventually stop working

chemistry one (8 decks)

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