Energy Changes Flashcards

1
Q

What is the conservation of
energy principle?

A

Energy is conserved in chemical reactions. The amount of energy in the universe
at the end of a chemical reaction is the same as before the reaction takes place

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2
Q

What is an exothermic
reaction? Give examples

A

A reaction where energy is transferred to the surroundings so that the
surroundings temperature increases – combustion, oxidation reactions and
neutralisation (acid + alkali) reactions. Negative sign of energy change.

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3
Q

What is an endothermic
reaction? Give examples

A

A reaction where energy is taken in from the surroundings so the surroundings
temperature decreases – thermal decomposition, reaction of citric acid and
sodium hydrogencarbonate. Negative sign of energy change.

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4
Q

What is activation energy?

A

Minimum amount of energy that particles need to react

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5
Q

What is a reaction profile?

A

Reaction profile is a graph which shows the relative energies of reactants and
product, as well as activation energy of the reaction.

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6
Q

What occurs in a chemical reaction in
terms of bond energies? Describe
exothermic and endothermic reactions in
terms of bond breaking/forming.
Higher Tier Only

A

Energy is supplied to break bonds and energy is released when bonds are made;
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

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7
Q

What is the equation to find
enthalpy change in terms of
bond energies?
Higher Tier Only

A

Energy of reaction = sum of bonds broken – sum of bonds made

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8
Q

What is a cell?

A

A cell is composed of two electrodes dipped in an electrolyte solution. It produces
electricity from a chemical reaction.

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9
Q

What is a battery?

A

A battery consists of two or more cells connected in series.

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10
Q

What determines the voltage
obtained from a cell?

A

Identities of metals used as electrodes and the identity and concentration of an
electrolyte.

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11
Q

State the advantages and
disadvantages of using cells
and batteries.

A

(+) more or less cheap, some are rechargeable, a convenient source of electrical
energy
(-) harmful chemicals

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12
Q

Describe rechargeable and
non-rechargeable cells

A

Rechargeable – chemical reactions are reversed when an external current is
supplied
Non-rechargeable – reactants are used up, cannot be recharged

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13
Q

What is a fuel cell? What is the
overall reaction in a hydrogen
fuel cell? What are the half
equations?
Reactions
Higher tier only

A

Fuel cells are supplied by fuel and oxygen to oxidise the fuel to generate
electricity.

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14
Q

What is the overall reaction in a
hydrogen fuel cell? What are the
half equations?

Reactions
Higher tier only

A

Cathode: 2 H2
→ 4 H+ + 4 e−
Anode: O2
+ 4 H+ + 4 e−→ 2 H2O
Overall: → 2 H2
+ O2
→ 2 H2O

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15
Q

What are the advantages and
disadvantages of hydrogen
fuel cells?

A

Advantages: no pollutants, no recharging
Disadvantages: flammable, H2
difficult to store, fossil fuel production, toxic
chemicals, expensive production of H2
by electrolysis

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