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Chemistry > Reactivity 1 > Flashcards

Reactivity 1 Flashcards

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1
Q

What happens to the energy in an exothermic reaction?

A

Excess energy is given out to the surroundings as heat

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2
Q

What happens to the energy in an endothermic reaction?

A

Excess energy required is taken in from the surroundings

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3
Q

Do exothermic reactions have a positive or negative ∆H value?

A

Negative

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4
Q

Do endothermic reactions have a positive or negative ∆H value?

A

Positive

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5
Q

What is ΔH⦵ measured in?

A

kJ mol^-1

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6
Q

What is ΔH⦵?

A

Standard enthalpy change

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7
Q

Is energy required to form a chemical bond?

A

No

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8
Q

Is energy required to break a chemical bond?

A

Yes

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9
Q

What is the formula to calculate enthalpy changes?

A

ΔH⦵ = ΔH⦵(bonds broken) - ΔH⦵(bonds formed)

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10
Q

If you are doing a simultaneous equation and you rearrange the formula, what happens to ΔH?

A

Reverse the sign

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11
Q

Arrange from strongest to weakest: single covalent bond, double covalent bond, triple covalent bond

A

Triple covalent, double covalent, single covalent

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12
Q

What is the idea with the Hess’ Law problems for the indirect determination of an enthalpy change? (triangles)

A

A going directly to C or through B

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13
Q

How do you find the bond enthalpy in the indirect determination of an enthalpy change?

A

Figure out the number of bonds broken, and divide previous answer by said number

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14
Q

Specific energy of a fuel formula

A

energy released from the fuel/mass of fuel consumed

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15
Q

Units for specific energy of a fuel

A

kJ kg^-1

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16
Q

If you know the enthalpy of combustion, how do you find the specific energy?

A

Dividing by the molar mass

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17
Q

Three main fossil fuels

A

Coal, crude oil, natural gas

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18
Q

How is oil and natural gas produced?

A

Anaerobic decomposition of marine organisms

19
Q

How is coal produced?

A

Terrestrial vegetation

20
Q

Advantages of natural gas

A

Clean, easily transported, higher specific energy than coal or oil

21
Q

Disadvantages of natural gas

A

Contributes to global warming, limited lifespan, uneven distribution

22
Q

Advantages of oil

A

Easily transported, feedstock for organic chemicals, convenient fuel for vehicles

23
Q

Disadvantages of oil

A

Contributes to global warming, limited lifespan, risk of marine pollution (oil spills)

24
Q

Advantages of coal

A

Present in large quantities, feedstock for organic chemicals, releases more energy than renewable sources, longer lifespan

25
Q

Disadvantages of coal

A

Contributes to global warming, not as easily transported, mining coal is dangerous, dirty

26
Q

What is the greenhouse effect?

A

Greenhouse gases absorbing some of the infrared heat from the earth and re-radiating it back into the earth.

27
Q

What is a carbon footprint?

A

Total amount of greenhouse gases produced during human activities

28
Q

What energy is converted in photosynthesis?

A

Light energy to chemical energy

29
Q

What is the photosynthesis equation?

A

6CO2 + 6H20 → C6H12O6

30
Q

What is biomass?

A

Organic material that can be used as an energy source

31
Q

How is liquid fuel obtained from biomass?

A

Fermentation

32
Q

What is the equation for obtaining liquid fuel from biomass?

A

C6H12O6 → 2C2H5OH + 2CO2

33
Q

What is gasohol composed of?

A

10% ethanol and 90% gasoline

34
Q

What is a common use for gasohol?

A

Used in unmodified cars, making them less reliant on crude oil.

35
Q

Advantages of biomass

A

Renewable and always available, doesn’t significantly contribute to the greenhouse effect, safer to produce, reduces landfill amount

36
Q

Disadvantages of biomass

A

Uses up land that could be used for animals, increases the use of fertilisers which could pollute water, removes nutrients from the soil, methods of conversion are small scale.

37
Q

In what form is the energy given out during the combustion of hydrogen in oxygen to form water?

A

Electricity (not heat)

38
Q

Do hydrogen fuel cells need an external source of electricity?

A

No

39
Q

What is the product of hydrogen fuel cells?

A

Water

40
Q

What are the electrolytes used in alkaline fuel cells?

A

NaOH or KOH

41
Q

What is used as the electrolyte in an acidic fuel cell?

A

An acid

42
Q

What is the overall reaction equation in alkaline and acidic fuel cells?

A

2H2 + O2 → 2H2O

43
Q

What are the products of a methanol fuel cell?

A

Carbon dioxide and water

44
Q

If a reaction is reversed, what happens to the ΔH value?

A

It switches (positive/negative, negative/positive)/changes the sign

Chemistry (5 decks)

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