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Unit 3/4 Chemistry > Chapter 2 Energy From Fuels > Flashcards

Chapter 2 Energy From Fuels Flashcards

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1
Q

What do all substances have?

A

Chemical energy

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2
Q

What is chemical energy comprised of?

A

Potential energy + kinetic energy in the substance

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3
Q

What does chemical energy result from? (MARRV)

A 
Movement of electrons
Attractions between electrons and protons
Repulsion between nuclei 
Repulsion between electrons 
Vibrations and rotations around bonds
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4
Q

Define chemical energy

A

Chemical energy is the sum of chemical potential energy and kinetic energy in a substance. Chemical energy is stored within the bonds between atoms and molecules, The energy results from things such as MARRV

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5
Q

Where is chemical energy stored?

A

Bonds between atoms and molecules

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6
Q

What is chemical energy sometimes referred to?

A

Enthalpy or heat content

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7
Q

How is enthalpy denoted

A

delta H

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8
Q

Define enthalpy

A

Also known as heat content. It is the sum of the chemical potential energy and kinetic energy in a substance.

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9
Q

Define enthalpy change

A

The difference in the total enthalpy of the products and the total enthalpy of the reactants denoted delta H. AKA heat of reaction.

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10
Q

Define enthalpy of combustion

A

The enthalpy change that occurs when mole of a compound is burned completely in oxygen, given the symbol delta Hc

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11
Q

What happens in chemical reaction most basically

A

Energy can be either absorbed from the surroundings or released to the surroundings

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12
Q

State the law of conservation of energy

A

Energy cannot be created or destroyed, however, it can change forms (Energy transformations - see fuels - chap 1 )

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13
Q

State the rule governing the law of conservation of energy.

A

TCE reactants = TCE products

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14
Q

Define the system

A

Chemical reaction

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15
Q

Define the surroundings

A

Everything excluding the system. Everything excluding the reaction itself.

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16
Q

Define an exothermic reaction

A

A reaction where energy is released to its surrounds; delta H is negative.

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17
Q

Define an endothermic reaction

A

A reaction where energy is absorbed from its surrounds; delta H is positive.

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18
Q

State the rule governing an exothermic reaction

A

TCE products < TCE reactants

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19
Q

Give the rule governing an endothermic reaction

A

TCE products > TCE reactants

20
Q

List 4 examples of endothermic reactions

A
  1. Melting
  2. Evaporation
  3. Sublimation
  4. Decomposition
21
Q

List 2 examples of exothermic reactions

A
  1. Condensation

2. Freezing

22
Q

How are endothermic and exothermic reactions represented

A

Using energy profile diagrams

23
Q

In an energy profile diagram, in terms of arrows, what way does the arrow point in an endothermic reaction?

A

Up as energy is absorbed (more is gained)

24
Q

In an energy profile diagram, in terms of arrows, what way does the arrow point in an exothermic reaction?

A

Down as energy is released (energy is lost)

25
Q

On an energy profile diagram for an endothermic reaction or exothermic reaction, where can the:

i) activation energy
ii) Delta H be found

A

i) Between reactants and highest peak

ii) Between reactants and products

26
Q

Define the activation energy

A

The minimum amount of energy required to break the bonds of all reactants to start a reaction.

27
Q

What to do in reverse reactions?

A

Swap everything (products = reactants, reactants = products, and exo=endo, endo=exo) Switch delta H sign too

28
Q

Define a thermochemical equation

A

A chemical equation that includes enthalpy change of the reaction

29
Q

What is the delta H in a thermochemical equation based/dependent on?

A

Stoichiometric rations in equation

30
Q

What is the unit for delta H

A

Kj/mol

31
Q

When is enthalpy measured

A

SLC

  • 25 degrees
  • 100Kpa
  • 298K
32
Q

What does a thermochemical equation show?

A

energy absorbed or energy released in a chemical reaction

33
Q

Define a combustion reaction

A

Combustion reactions are rapid reactions with oxygen accompanied by the release of large amounts of energy.

34
Q

Are all combustion reactions exothermic?

A

Yes, they are! They all release heat/thermal energy.

35
Q

Is combustion a redox reaction?

A

Yes!

36
Q

What is a redox reaction?

A

Involves the simultaneous transfer of electrons from one species to another and thus oxidation numbers change)

37
Q

When does complete combustion occur?

A

When O2(g) is in excess

38
Q

What are the products of complete combustion?

A

CO2 and H20

39
Q

When does incomplete combustion occur?

A

When O2(g) is limited

40
Q

What are the products of incomplete combustion?

A

CO and/or C + H20

41
Q

Define the heat of combustion

A

The enthalpy change that occurs when a specified amount if the fuel burns completely in oxygen.

42
Q

How is the heat of combustion measured?

A

Using a calorimeter

43
Q

When is the heat of combustion measured?

A

Under SLC

44
Q

Which substances have the units kj/mol and Kj/g respectively for the heat of combustion?

A

Pure and then impure substances

45
Q

How is energy found?

A

E=n x delta Hc

46
Q

How do you find the energy content by gram

A

delta Hc per mole / Molar mass

47
Q

How do you find the energy content by tonne

A

1 Kj/g = 10^3 MJ/tonne

Unit 3/4 Chemistry (2 decks)

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