Unit 1 - Chemical Changes & Structure

Question 1

What is collision theory?

Answer 1

Collision theory is the conditions required for particles to react and make more ‘successful’ collisions

Question 2

A successful collision means a particle will…

3 things

Answer 2

Collide frequently
Collide in correct alignment
Have enough energy to overcome activation energy

Question 3

What is activation energy

Answer 3

The minimum kinetic energy needed by colliding particles in order for a chemical reaction to take place

Question 4

How fast would the rate of a reaction be if it had a high Ea

Answer 4

Slow

Question 5

How fast would the rate of a reaction be if it had a low Ea

Answer 5

Fast

Question 6

How does a catalyst speed up a chemical reaction

Answer 6

A catalyst speeds up a chemical reaction by lowering Ea. It does not get involved or used up.

Question 7

What does a potential energy diagram tell

Answer 7

If a reaction is endothermic
If a reaction is exothermic
Where the activated complex is
Ea
Enthalpy change

Question 8

How do you tell if a reaction is endothermic from a potential energy diagram

Answer 8

It ends with more energy showing that it had gained energy

Question 9

How do you know of a reaction is exothermic from a potential energy diagram

Answer 9

It ends with less energy showing that or has released energy

Question 10

How do you calculate enthalpy change

Answer 10

Product-reactants

Question 11

How do you calculate activation energy

Answer 11

Highest point-reactant energy

Question 12

What is activated complex

Answer 12

The activated complex is the arrangement of atoms produced when old and new bonds are breaking and forming. It is a highly unstable arrangement of atoms that exists for a fraction of a second

Question 13

What is the effect of concentration on rate of reaction

Answer 13

The more reactant particles present the more successful collisions so faster rate
These reacting particles have enough kinetic energy to overcome activation energy

Question 14

What is the effect of temperature on taste of reaction

Answer 14

As temperature increases reaction rate increases
This is because temperature increases makes particles move faster, they have more successful collisions and have enough energy to overcome Ea

Question 15

What is temperature

Answer 15

Temperature is a measure of the average kinetic energy of particles in a substance

Question 16

Which reaction rate is higher, graph 1 or graph 2? Why?

Answer 16

The rate of reaction in graph2 is higher than in graph 1 because there is less energy required to overcome activation energy increasing the number of successful collisions

Question 17

What is the only thing that can change the position of Ea

Answer 17

A catalyst

Question 18

Why are atoms in metallic bonding tightly packed

Answer 18

Because the delocalised electrons are moving from atom to atom
This strong electrostatic attraction between the positive nucleus and the delocalised electrons creates a strong bond which acts in all directions around each atom

Question 19

What is the relationship between boiling point and alkali metals

Answer 19

As the atomic number increases the boiling point decreases
Because:
Down group 1 energy levels increases
Positive nucleus has a weaker hold on outer electrons
Less energy required to break the bond
Boiling point value decreases

Question 20

What is the relationship between period 4 and the boiling point

Answer 20

As atomic number increases the boiling point increases
Because:
Across period 4 electrons don’t increase but number of electrons in outer shell does
Positive nucleus has a stronger hold on the outer electrons
More energy is required to break the bond
Boiling point value increases

Question 21

What are the types of molecular forces

Answer 21

Intermolecular and intermolecular

Question 22

What are intermolecular forces

Answer 22

Between molecule

these are weak

Question 23

What are intermolecular forces

Answer 23

Within molecules

These are strong

Question 24

What is a molecule

Answer 24

A small covalent compound

Question 25

What are LdF’s

Answer 25

London dispersion forces are formed from electron wobble. This forms temporary dipoles. These are the weakest of all WdW forces. Not much energy is required to break them

Question 26

What is the relationship between boiling point and the noble gasses

Answer 26

``` As the atomic number increases the boiling point increases Because: Down the group there is more electrons More e- = more e- wobble More e-wobble = more temporary dipoles Stronger LdF’s = more energy to break ```

Question 27

What is the relationship of atomic size as it goes down a group

Answer 27

As you go down a group the atomic size increases as there is an extra electron shell

Question 28

What is the relationship of atomic size as you go along a period

Answer 28

There is a positive charge on the nucleus. It had a pulling effect on the outer electron level bringing the levels closer so atomic size decreases

Question 29

What is ionisation

Answer 29

This is the energy required to remove an electron from the atom of an element in a mole of free atoms

Question 30

How many times can sodium be ionised

Answer 30

11 times | Because it has 11 e-

Question 31

What is the relationship between halogen size and melting point

Answer 31

As the halogen size increases the melting point increases Because: The bigger the halogen the more electron levels which means stronger London Forces. This means more energy is needed to break those bonds

Question 32

What is the relationship between increasing the number of atoms of hydrocarbons and melting point

Answer 32

The atomic size remains the same as the hydrocarbons only contain hydrogen and carbon There are more atoms which means more e- wobble This means stronger LdF’s Which means more energy is needed to break attraction

Question 33

What is electronegativity

Answer 33

Electronegativity is the measure of attraction of covalently bonded electrons between atoms