Developing fuels

Question 1

Define enthalpy change.

Answer 1

Its the quantity of energy transferred to or from the surroundings when the reaction is carried out in an open container.

Question 2

Define endothermic reactions.

Answer 2

A reaction that takes in energy into the system from the surroundings, the temperature of the surroundings decreases. Enthalpy change is positive.

Question 3

Define exothermic reactions.

Answer 3

A reaction that gives out energy from the system to the surroundings, the temperature of the surroundings increases. Enthalpy change is negative.

Question 4

What processes are breaking and forming chemical bonds?

Answer 4

-breaking bonds=endothermic process(requires energy)
-forming bonds=exothermic process(releases energy)

Question 5

What is ‘standard enthalpy change’?

Answer 5

Enthalpy change that is measured under standard conditions.

Question 6

What are the 4 types of enthalpy change? Write their symbols.

Answer 6

-Standard enthalpy change of reaction
-Standard enthalpy change of combustion
-Standard enthalpy change of formation
-Standard enthalpy change of neutralisation

Question 7

What are the standard conditions?

Answer 7

-1ATM/atmosphere pressure
-concentration of 0.1mol/dm-3
-25degreesC [298K]

Question 8

Define ‘standard enthalpy change of reaction’

Answer 8

The enthalpy change for a reaction that occurs between the number of moles of the reactants.

Question 9

Define ‘standard enthalpy change of combustion’

Answer 9

The enthalpy change that occurs when 1 mole of a substance burns completely in oxygen under standard conditions.

Question 10

Define ‘standard enthalpy change of formation’

Answer 10

The enthalpy change when 1 mole of a compound is formed from its elements under standard conditions.

Question 11

Define ‘standard enthalpy change of neutralisation’

Answer 11

The enthalpy changethat occurs when 1 mole of hydrogen ions react with 1 mole of hydroxide ions to form 1 mole of water under standard conditions and in solutions with a concentration of 1mol/dm-3

Question 12

What does Hess’s law state?

Answer 12

States that as long as the starting and finishing points are the same, the enthalpy change for a chemical reaction will always be the same.

Question 13

Define ‘activation energy’

Answer 13

The minimum amount of energy required to start a reaction.

Question 14

What is energy density?

Answer 14

The energy produced in KJ when 1Kg of fuel is burned.

Question 15

Why can carbon form so many compounds?

Answer 15

-covalent bonds are strong
-forms 4 covalent bonds
-branched structure
-ring structure

Question 16

What does a structural formula show?

Answer 16

Shows all atoms and bonds in the molecule/ full structure

Question 17

What does a skeletal formula show?

Answer 17

Uses lines to represent the shape of the hydrocarbon framework, C and H atoms are not shown.

Question 18

What is the functional group of an alcohol?

Answer 18

OH

Question 19

What does the functional group do?

Answer 19

Determines the chemistry of the compound.

Question 20

What is a homologous series?

Answer 20

A group of organic compounds that have the same functional group.

Question 21

Describe the features of a homologous series.

Answer 21

-same molecular formula
-similar properties b/c same functional group
-physical properties change as molecules become larger

Question 22

What is a hydrocarbon?

Answer 22

Compounds that are made of H and C atoms only.

Question 23

Compare alkanes and alkenes.

Answer 23

Alkanes:
-CnH2n+2
-saturated(single bond)
-name ends in -ane
-aliphatic(don’t contain benzene rings)

Alkenes:
-CnH2n
-unsaturated(double bond)
-names ends in -ene
-aliphatic(don’t have delocalised benzene ring structures)

Question 24

Describe cycloalkanes.

Answer 24

-CnH2n
-name ends in -ane
-saturated(single bond)
-not aromatic(no benzene ring)
-aliphatic

Question 25

Define standard molar bond enthalpy.

Answer 25

The energy needed to break 1 mole of covalent bonds in the gaseous state.

Question 26

Describe the relationship between bond enthalpy and bond length.

Answer 26

As length decreases the bond enthalpy increases.

-short bonds=stronger
-long bonds=weaker

Question 27

2 problems with fractional distillation of crude oil.

Answer 27

-in high demand
-finite resource

Question 28

What is cracking?

Answer 28

The breaking up of large alkane molecules into smaller alkanes and alkenes.

Question 29

Describe thermal and catalytic cracking.

Answer 29

Thermal cracking:
Carried out by heating the alkane at 900degrees for 1second in the presence of steam.

Catalytic cracking:
Alkane is passed over a zeolite catalyst at 450degrees.

Question 30

Why is catalytic cracking better for the environment than thermal cracking?

Answer 30

Better b/c less energy needed.

Question 31

What is a catalyst?

Answer 31

Its a substance which alters the rate of a chemical reaction without itself undergoing a permanent change.

Question 32

How do catalysts increase the rate of reaction?

Answer 32

It increases the rate of reaction by providing an easier route for the reaction.

Question 33

What is a zeolite?

Answer 33

Aluminosilicate compounds that have regular framework structures with pores similar to size to hydrocarbons.

Ideal as a catalyst b/c of spaces/gaps and layers so reactant can be easily absorbed.

Question 34

Describe heterogenous catalysis.

Answer 34

When the state of the catalyst is different to the reactants state.

1.reactants absorb onto surface of catalyst
2.bonds in reactants begin to break
3.new bonds start to form in products
4.products are diffused from surface of catalyst

Question 35

Describe homogeneous and heterogeneous catalysts.

Answer 35

-homogeneous=states in catalyst and reactants are the same
-heterogeneous=states in catalyst and reactants are different

Question 36

What is produced when any 2 atomic orbitals overlap ‘head on’?

Answer 36

A sigma molecular orbital

Question 37

What is produced when 2 p atomic orbitals overlap ‘side on’?

Answer 37

A pi molecular orbital

Question 38

1.All single bonds are ________.
2.All double bonds are ________.

Answer 38

1.sigma molecular orbitals
2.sigma and pi molecular orbitals