Topic 5 Energy Change Flashcards

1
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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2
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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3
Q

What is activation energy?

A

Minimum amount of energy that particles need to react

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4
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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5
Q

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

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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6
Q

What is the equation to find energy change in terms of bond energies?

A

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

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7
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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8
Q

What is a battery?

A

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

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9
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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10
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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11
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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12
Q

What is a fuel cell?

A

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

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13
Q

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

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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14
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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