Unit 1 - Chemical changes and structures

Question 1

What two things determine whether a reaction is successful or not?

Answer 1

Collision Geometry and energy of collision.

Question 2

What can the effect of surface area have on the rate of reaction?

Answer 2

Increasing the surface area (or decreasing the particle size - both mean the same thing) increases the chance of successful collision and therefore increases the rate of reaction. The opposite applies if the surface area is decreased.

Question 3

What can the effect of concenctration have on the rate of reaction?

Answer 3

Increasing the concentration of a solution increases the number of particles in the same volume. Therefore there is more chance of successful collision which therefore means increased rate of reaction.

Question 4

What can the effect of temperature have on the rate of reaction?

Answer 4

Raising the temperature increases the kinetic energy of ALL the particles, they collide with greater force (and more frequently). Therefore increasing the rate of reaction.

Question 5

What is ‘Activation Energy’ (Ea)?

Answer 5

Activation energy is the minimum kinetic energy required by the colliding particles. This activation energy varies for each reaction.

Question 6

What is meant by the term, ‘First ionisation energy’?

Answer 6

First ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in a gaseous state.

Question 7

In first ionisation energy, what is the first electron to be removed and why?

Answer 7

The outermost electron because it is the most weakly held

Question 8

Going across a period, what happens to the ionisation energy and why?

Answer 8

Going across a period, the ionisation energy increases because the nuclear charge increases and holds the outer electrons more strongly and therefore more energy needs to be supplied to remove the electron.

Question 9

Going down a group, what happens to the ionisation energy and why?

Answer 9

Going down a group, the ionisation energy decreases. This is because the outer electrons are further away from the nucleus meaning they are more weakly held.

Question 10

Why does going down a group decrease the ionisation energy despite the increase in nuclear charge?

Answer 10

The screening effect of the inner electron shells reduces the nuclear attraction for the outer electrons, despite the increased nuclear charge.
Also the outermost electron is further away from the nuclear attraction.

Question 11

What is ‘the screening effect?

Answer 11

Electron screening is when inner electrons reduce the attraction of the nucleus for the outer electrons. The screening effect will increase as the number of inner energy levels increase.

Question 12

Why is the second ionisation energy of an element always greater than the first ionisation energy?

Answer 12

In the second ionisation energy negative electrons are being removed from positive ions rather than neutral atoms. In the positive ion there is a greater attraction for the electrons so more energy is needed to remove the second mole of electrons.

Question 13

Why is the second ionisation energy of potassium (K) much greater than the second ionisation energy of calcium (Ca)?

Answer 13

The second ionisation energy of K involves removing an electron from a stable electron arrangement - which requires a lot of energy.

The second ionisation energy of calcium involves removing an electron to form a stable electron arrangement - which requires a lot less energy.

Question 14

What is electronegativity?

Answer 14

Electronegativity is a measure of an atom’s attraction for the shared pair of electrons in a bond.

Question 15

Why does electronegativity increase across a period?

Answer 15

Nuclear charge increases (more protons) which means there is a greater attraction for bonding electrons

Question 16

Why does electronegativity decrease down a group?

Answer 16

The positive charge of the nucleus is further away from the bonding electrons and is shielded by the extra electron shells.

Question 17

How do you work out the enthalpy change from a reaction pathway diagram?

Answer 17

The distance between the reactants and products. (Exothermic will be negative, endothermic will be positive)

Question 18

How do you work out the activation energy from a reaction pathway diagram?

Answer 18

The distance from the reactants to the top of the peak in the diagram.

Question 19

In a reaction pathway diagram, how do you know is the reaction is endothermic?

Answer 19

The reactants will be lower than the products/ enthalpy change is positive.

Question 20

In a reaction pathway diagram, how do you know is the reaction is exothermic?

Answer 20

The reactants are higher than the products/ enthalpy change is negative.

Question 21

Why are temporary dipoles temporary in London Dispersion Forces?

Answer 21

The dipoles are only temporary as electron repulsion quickly act to ensure a more even distribution, causing a brief ‘wobble’ in the atom which affects the electron clouds in another atom - causing short lived attractions between the slightly positive side of one atom and the slightly negative side of another. (The electrons are continually moving).

Question 22

What effect does the size of an atom have on the strength of London Dispersion Forces?

Answer 22

Increases as the size of the atom increases because there are more electrons.

Question 23

State two conditions necessary for a collion to be successful?

Answer 23

• Molecules most collide with energy greater than or equal to the activation energy.
• Molecules most have correct collision geometry.

Question 24

Out of the following, what is not an example of a Van Der Waals’ force?

• Covalent Bonding
• Hydrogen Bonding
• London Dispersion Forces
• Permanent dipole-permanent dipole interactions

Answer 24

Covalent bonding

Question 25

True or false: A catalyst provides energy so that the molecules have successful collions.

Answer 25

False. A catalyst lowers the activation energy by providing an alternative route for the reaction.

Question 26

What is the ion-electron equation for the first ionisation energy of sodium?

Answer 26

Na(g) –> Na(g)+ + e-

Question 27

What is a van der Waals force?

Answer 27

Any intermolecular force of attraction that exists between atoms/molecules. Examples include LDF, permanent dipole-permanent dipole interactions and Hydrogen bonding.

Question 28

Why can a small increase in temperature lead to a large increase in reaction rate?

Answer 28

Increasing the temperature increases BOTH the kinetic energy of the particles (increasing energy of collision) AND the frequency of collisions.

Question 29

What type of bonding and structure is present in silicon?

Answer 29

Covalent network.

Question 30

What is metallic bonding?

Answer 30

Metallic bonding is the type of bonding found in metallic elements. This is the electrostatic force of attraction between positively charged ions and delocalised outer electrons.

Question 31

What is pure covalent bonding?

Answer 31

Atoms in a covalent bond are held together by electrostatic forces of attraction between positively charged nuclei and negatively charged shared electrons.

Question 32

Can a molecule be described as polar if it has a permanent dipole - permanent dipole interactions?

Answer 32

Yes because a permanent dipole is due to a difference in electronegativity between the atoms in a covalent bond.

Question 33

What is hydrogen bonding?

Answer 33

Hydrogen bonding is a stronger form of permanent dipole - permanent dipole interactions. Although it is stronger than the permanent dipole interactions, it is weaker than a covalent bond.

Question 34

What is a metallic structure and name an element which has such?

Answer 34

A metallic structure consists of a giant lattice of positively charged ions and delocalised outer electrons. Any metallic element will have a metallic structure,

Question 35

What is a covalent molecular structure and name an element which has such?

Answer 35

A covalent molecular structure consists of discrete molecules held together by weak intermolecular forces, such as Van der Waal’s forces and hydrogen bonds. Element

Question 36

What is a monatomic structure?

Answer 36

A monatomic structure consists of discrete atoms held together by Van der Waals’ forces, such as the Noble gases.

Question 37

If a substance can be described as polar, will it be soluble in a polar solvent (such as water)?

Answer 37

Yes.

Question 38

If a substance can be described as non-polar, will it be soluble in a polar solvent (such as water)?

Answer 38

No.

Question 39

In the diatomic molecules - and phosphorus and sulfur - what is the structure of the molecules?

Answer 39

Discrete covalent

Question 40

What is the structure present in boron, carbon and silicon?

Answer 40

Covalent networks.

Question 41

What is meant by permanent dipole - permanent dipole attraction?

Answer 41

Permanent dipole - permanent dipole interactions are additional electrostatic forces of attraction between polar molecules.

Question 42

How do permanent dipole - permanent dipole attractions arise?

Answer 42

They arise when the difference in electronegativity is not zero.