Chapter 2 Energy From Fuels

Question 1

What do all substances have?

Answer 1

Chemical energy

Question 2

What is chemical energy comprised of?

Answer 2

Potential energy + kinetic energy in the substance

Question 3

What does chemical energy result from? (MARRV)

Answer 3

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

Question 4

Define chemical energy

Answer 4

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

Question 5

Where is chemical energy stored?

Answer 5

Bonds between atoms and molecules

Question 6

What is chemical energy sometimes referred to?

Answer 6

Enthalpy or heat content

Question 7

How is enthalpy denoted

Answer 7

delta H

Question 8

Define enthalpy

Answer 8

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

Question 9

Define enthalpy change

Answer 9

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

Question 10

Define enthalpy of combustion

Answer 10

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

Question 11

What happens in chemical reaction most basically

Answer 11

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

Question 12

State the law of conservation of energy

Answer 12

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

Question 13

State the rule governing the law of conservation of energy.

Answer 13

TCE reactants = TCE products

Question 14

Define the system

Answer 14

Chemical reaction

Question 15

Define the surroundings

Answer 15

Everything excluding the system. Everything excluding the reaction itself.

Question 16

Define an exothermic reaction

Answer 16

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

Question 17

Define an endothermic reaction

Answer 17

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

Question 18

State the rule governing an exothermic reaction

Answer 18

TCE products < TCE reactants

Question 19

Give the rule governing an endothermic reaction

Answer 19

TCE products > TCE reactants

Question 20

List 4 examples of endothermic reactions

Answer 20

1. Melting
2. Evaporation
3. Sublimation
4. Decomposition

Question 21

List 2 examples of exothermic reactions

Answer 21

1. Condensation

2. Freezing

Question 22

How are endothermic and exothermic reactions represented

Answer 22

Using energy profile diagrams

Question 23

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

Answer 23

Up as energy is absorbed (more is gained)

Question 24

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

Answer 24

Down as energy is released (energy is lost)

Question 25

On an energy profile diagram for an endothermic reaction or exothermic reaction, where can the: i) activation energy ii) Delta H be found

Answer 25

i) Between reactants and highest peak | ii) Between reactants and products

Question 26

Define the activation energy

Answer 26

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

Question 27

What to do in reverse reactions?

Answer 27

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

Question 28

Define a thermochemical equation

Answer 28

A chemical equation that includes enthalpy change of the reaction

Question 29

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

Answer 29

Stoichiometric rations in equation

Question 30

What is the unit for delta H

Answer 30

Kj/mol

Question 31

When is enthalpy measured

Answer 31

SLC - 25 degrees - 100Kpa - 298K

Question 32

What does a thermochemical equation show?

Answer 32

energy absorbed or energy released in a chemical reaction

Question 33

Define a combustion reaction

Answer 33

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

Question 34

Are all combustion reactions exothermic?

Answer 34

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

Question 35

Is combustion a redox reaction?

Answer 35

Yes!

Question 36

What is a redox reaction?

Answer 36

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

Question 37

When does complete combustion occur?

Answer 37

When O2(g) is in excess

Question 38

What are the products of complete combustion?

Answer 38

CO2 and H20

Question 39

When does incomplete combustion occur?

Answer 39

When O2(g) is limited

Question 40

What are the products of incomplete combustion?

Answer 40

CO and/or C + H20

Question 41

Define the heat of combustion

Answer 41

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

Question 42

How is the heat of combustion measured?

Answer 42

Using a calorimeter

Question 43

When is the heat of combustion measured?

Answer 43

Under SLC

Question 44

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

Answer 44

Pure and then impure substances

Question 45

How is energy found?

Answer 45

E=n x delta Hc

Question 46

How do you find the energy content by gram

Answer 46

delta Hc per mole / Molar mass

Question 47

How do you find the energy content by tonne

Answer 47

1 Kj/g = 10^3 MJ/tonne