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Higher Chemistry > Unit 1 - Chemical changes and structure > Flashcards

Unit 1 - Chemical changes and structure Flashcards

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1
Q

Why is it important that chemists can control the rate of a reaction?

A

So that it is economically viable and safe

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2
Q

What happens to the reaction rate as reactants are used up?

A

It will decrease

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3
Q

What formula is used to calculate the average rate of a reaction?

A

Average rate = change in quantity/change in time

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4
Q

What is relative rate?

A

The rate of a reaction at any one point in time

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5
Q

What formula is used to work out the relative rate?

A

Relative rate = 1/t

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6
Q

What is the unit for average rate?

A

Gs-1, Mgs-1, kgs-1, mols-1 or cm3s-1 etc…

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7
Q

What is the unit for relative rate?

A

S-1

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8
Q

What is collision theory?

A

The theory that for a reaction to occur reactant molecules must: collide with enough energy to overcome repulsive forces and the molecules must be facing the right way.

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9
Q

Name 4 factors that can alter the rate of a reaction.

A

Temperature
Concentration
Particle size
Use of a catalyst

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10
Q

How does an increase in temperature affect the rate of a reaction?

A

The particles gain more kinetic energy and move more quickly. This increases the number of collisions so increases the rate of reaction.

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11
Q

How does an increase in concentration affect the rate of a reaction?

A

There is an increased number of particles in the reaction causing more collisions. This then causes an increase in the rate of a reaction.

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12
Q

How does decreasing the particle size affect the rate of a reaction?

A

It increases the surface area of the particles meaning there is a greater area for collisions to take place. Increasing the rate of reaction.

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13
Q

How does the addition of a catalyst affect the rate of a reaction?

A

Catalysts provide a surface for reactions to take place. Holding the molecules at a favourable angle increasing the likelihood of collisions. Increasing the rate of reaction.

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14
Q

What is activation energy?

A

The minimum energy required for a reaction to occur

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15
Q

On an energy diagram which particles have enough energy to react?
A. All of them
B. All before the activated complex
C. All of them before and up to the activated complex
D. All of them after the activated complex

A

D. All of the after the activated complex

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16
Q

Name 2 catalysts and there uses in the industry

A

Iron- making ammonia in the haber process

Platinum - making nitric acid in the Ostwald process

Rhodium and platinum- used in catalytic converters

Nickel- to harden vegetable oil when making margarine

Vanadium(v) oxide- in the contact process to make sulphuric acid

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17
Q

What do catalyst do?

A

Alters the rate of reaction allowing it to take place at lower temperatures, without being used up.

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18
Q

What enthalpy? (H)

A

The heat stored by a substance

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19
Q

On a potential energy diagram, if the reactants have more energy than the reactants. What type of reaction is it?

A

Exothermic. Heat energy is being lost.

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20
Q

On a potential energy diagram, if the products have more energy that the reactants what type of reaction is it?

A

Endothermic. Heat energy is being gained

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21
Q

What is the activated complex?

A

A high energy intermediate state where bonds are breaking and forming

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22
Q

On a potential energy diagram, if a catalyst is used will it’s pathway be:
A. The same as without
B. Higher up on the diagram than with out
C. Lower on the diagram than without

A

C. Lower that without. It allows reactions to take place with less energy

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23
Q

On a potential energy diagram, when a catalyst is used will the enthalpy change:
A. Increase
B. Stay the same.
C. Decrease

A

B. Increase. Catalysts don’t affect the reactants or products

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24
Q

What is the covalent radius?

A

A measure of how large individual atoms are. It shows different trends if you are moving across a period or down a group.

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25
Q

Why does the covalent radius decrease as you Move across a period?

A

As you move from left to right atoms have more electrons in their outer shell and protons in their nucleus. The Great attraction pulls the atom closer together making it smaller.

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26
Q

Why does the covalent radius increase as you move down a group?

A

There is extra outer shells causing the screening effect as the electrons are further away from the nucleus. Meaning the atom isn’t as pulled together.

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27
Q

What is ionisation energy?

A

The energy required to remove one mole of electrons from one mole of atoms in a gaseous state

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28
Q

Why are the subsequent ionisation energies higher than the first for most atoms?

A

Because electrons are being removed from full shells.

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29
Q

Why is ionisation energy greater as you move across a period?

A

Because of the increase in atomic charge having a greater pull on electrons

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30
Q

Why is ionisation energy decreasing as you move down a group?

A

Because the outer electrons are further away from the nucleus so there is less attraction

31
Q

What is electronegativity?

A

A measure of an atoms attraction for the electrons in a bond

32
Q

Why does electronegativity increase across a period?

A

Because atoms have a greater charge in there nucleus and a smaller covalent radius. Allowing a stronger bond to the bonding electrons

33
Q

Why does electronegativity decrease going down a group?

A

Because of the increased covalent radius the electrons are further away from the nucleus meaning that there is less attraction

34
Q

What is the element with the highest electronegativity?

A

Fluorine

35
Q

Describe a covalent bond

A

The result of 2 positive nuclei being held together by their common attraction for a shared pair of electrons

36
Q

Describe an ionic bond

A

An electrostatic force of attraction between positively charged ions

37
Q

Describe the strength of an ionic bond

A

A strong force of attraction which takes a lot of energy to break

38
Q

Describe a polar covalent bond

A

A bond where the atoms have a difference in electronegativity. So the electrons in the bond are pulled closest to the atom with the greatest electronegativity.

One atom becomes slightly positive and one slightly negative.

39
Q

What’s another name for a polar covalent bond?

A

A permanent dipole

40
Q

What attributes define a polar molecule?

A

Having a permanent dipole

If the spatial arrangements for the polar bonds allow the molecule to be polar

If there is a slight -ve and +ve charge in 2 sides of the molecule

41
Q

Describe a pure covalent bond

A

Bonding electrons are shared equally. The electronegativity’s are equal or almost equal

42
Q

What lies between pure covalent and ionic bonding on a bonding continuum?

A

Polar covalent bonding

43
Q

What happens if an electronegativity difference is close to 2?

A

Ions are formed

44
Q

What are the properties of a covalent network?

A

All atoms are joined by strong intermolecular covalent bonds

They have HIGH melting and boiling points

It requires a lot of energy to break

Insoluble in water

45
Q

What are different forms of an element called?

A

Polymorphs

46
Q

What are the 2 most common polymorphs of carbon?

A

Diamond and graphite

47
Q

How are carbon atoms arranged to make diamond?

A

Tetrahedrally around each other in a giant covalent network

48
Q

Why does diamond have a high meeting and boiling point?

A

Due to strong covalent bonds

49
Q

Why can’t diamond conduct electricity?

A

Because all 4 electrons in the outer shell are shared with other carbon atoms so there are not free electrons

50
Q

Why is graphite soft?

A

Because it’s atoms are arranged in layers, between which there are weak intermolecular forces

51
Q

Why can graphite conduct electricity?

A

Because only 3 out of 4 of its outer shell electrons are shared with other atoms so there are DELOCALISED electrons in the structure

52
Q

What is a covalent molecular element?

A

Small numbers of atoms joined by covalent bonds

53
Q

Can discrete covalent molecules conducts electricity?

A

No there are no free electrons or charged particles

54
Q

Why do discrete covalent molecules have love melting and boiling points?

A

Due to weak intermolecular forces between atoms

55
Q

Can ionic compounds conduct electricity?

A

Only in solution

56
Q

Do ionic compounds have high or low melting and boiling points?

A

HIGH due to strong ionic bonds

57
Q

Do metallic compounds have High or low melting and boiling points?

A

Mainly HIGH due to many intermolecular forces with the exception of mercury

58
Q

How does intermolecular forces relate to the viscosity of a substance?

A

The more intermolecular forces the more viscose the substance

59
Q

What would happen to discrete molecular elements if there were no intermolecular forces?

A

They would be gases at room temp.

60
Q

What are the intermolecular forces that occur between all molecules called?

A

Van Der Waals forces

61
Q

What are the 3 types the Van Der Waals forces?

A

London Dispersion Forces

Permanent dipole-permanent dipole interactions

Hydrogen bonding

62
Q

What is a London dispersion force?

A

An attraction due to the constant motion of electrons

63
Q

What Van Der Waal force exists between all molecules?

A

London dispersion forces

64
Q

What will London dispersion forces do to the charge of an atom/molecule?

A

Cause a temporary concentration of charge on one side of the atom/molecule

65
Q

What is induced in non-polar molecules due to electron movements?

A

A temporary dipole

66
Q

What are the weakest forces that exist between molecules?

A

London dispersion forces

67
Q

What happens to neighbouring molecules when next to a temporary dipole in a non polar element?

A

Similar but opposite forces are induced causing momentary weak attractions

68
Q

What deciphers the strength of a London dispersion force?

A

The number of electrons within an atom/molecule

69
Q

Where do permanent dipole to permanent dipole interactions happen?

A

Where there are polar covalent bonds?

70
Q

Are permanent dipole to permanent dipole interactions stronger or weaker than London dispersion forces?

A

Weaker

71
Q

What is hydrogens bonding?

A

Bonds consisting of a hydrogen atom bonded to to an atom of a strongly electronegative element such as F, O or N

72
Q

What name is given to electrostatic forces of attraction between molecules that contain highly polar bonds?

A

Hydrogen bonding

73
Q

What is the strongest Van Der Waal force?

A

Hydrogen bonding

74
Q

What is stronger a covalent bond or a hydrogen bond?

A

A hydrogen bond

Higher Chemistry (3 decks)

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