Changes and structure

Question 1

What are the two key things needed for a reaction to be successful?

Answer 1

Activation energy and/or correct collision geometry

Question 2

How can temperature be linked with the kinetic energy of a reaction?

Answer 2

Temperature can be regarded as a measure of the kinetic energy of all the particles present in the reaction.
It only requires a small rise in temperature can double the rate of reaction

Question 3

What is the ratio between rate of reaction and concentration?

Answer 3

When concentration is doubled so too is rate of reaction

Question 4

What do catalysts do?

Answer 4

Lower the activation energy of a reaction

Question 5

How do you calculate average rate of reaction?

Answer 5

Time interval (t2-t1)

Question 6

What is the difference between homogenius and hetrogenius catalysts?

Answer 6

Homogenius catalysts are in the same physical state as the reactants while hetrogenius catalysts are in a different state

Question 7

Enthalpy change?

Answer 7

Products - reactants (- = exothermic, + = endothermic)

Question 8

What is the activation complex?

Answer 8

An unstable arrangement of atoms formed at the maximum of the potential barrier during a reaction

Question 9

What is the ionisation energy?

Answer 9

Energy required to remove one mole of electrons from one mole of atoms in the gaseous state

Question 10

Why does the first ionisation energy increase across a period?

Answer 10

Because as the atoms decrease in size across a the table the outermost electrons are nearer the protons/nucleus and so are more strongly attracted.

Question 11

Why does the first ionisation energy decrease down a group?

Answer 11

Because as the atoms increase in size going down a group the outermost electrons are further away from the protons/nucleus and so they are less strongly held.

Question 12

What is the electronegativity of an atom?

Answer 12

A measure of its pulling power/attraction for the shared electrons in a covalent bond. Elements in top right have strongest attraction while bottom left has weakest.

Question 13

How does polarity occur within compounds?

Answer 13

If difference is > or = 0.4 then polarity occurs (the greater the electronegativity difference, the greater the ionic character).

Question 14

How are ionic bonds held together?

Answer 14

Ions in a lattice are held together by the strong electrostatic forces of attraction between the positive and negative ions.

Question 15

What are London dispersion forces?

Answer 15

Weakest form of intermolecular bond. Occur because the movement of electrons in the atoms and molecules causes a temporary dipole charge in one particle. this in turn causes an induced dipole in a nearby particle. The very small positive and negative charges produced then attract each other, so this is an electrostatic force of attraction.

Question 16

The larger the molecule (or atom) the stronger the LDF are and the more energy needed to break them.

Answer 16

Yes.

Question 17

Another calculate for rate of reaction

Answer 17

1 1
Rate = —– time = ——–
t rate

Question 18

What is hardening?

Answer 18

Breaking double bonds in unsaturated fats with hydrogen (in presence of nickel catalyst).

Question 19

What is covalent radii?

Answer 19

Half the distance between the nuclei of atoms joined by a covalent bond.

Question 20

What is ionic radii?

Answer 20

Half the distance between the inter-nuclear distance of what are effectively ions. (effectively radius of atom).

Question 21

What is Markownikoff’s rule?

Answer 21

In adding a compound, in the form H-X, to an unsymmetrical alkane, the hydrogen will always go to the carbon atom with the most number of hydrogen atoms.

Question 22

What is the trend in atomic radius across a period and why?

Answer 22

Decreases as the charge of the nucleus increases while the number of filled electron shells remain the same. Therefore the outer electrons are more strongly attracted to the nucleus.

Question 23

What is the trend in atomic radius down a group and why?

Answer 23

Increases as, despite an increase in nuclear charge, the further down you go the more filled electron shells. These shells shield the force of attraction between the nucleus and the outer electrons allowing them to be further away.

Question 24

Trends of electronegativity in the periodic table?

Answer 24

Down a group = decreases
Across a period = increases

This occurs due to the same factors which affect atomic radius.

Question 25

Trend for ionisation energy in periodic table?

Answer 25

Down a group = decreases
Across a period = increases

Same reasons as other two.

Question 26

What are the four main characteristics of compounds that can be used help decide the type of bonding present?

Answer 26

1. Ionic will conduct when molten or in solution
2. Ionic will have high melting point as ionic lattice is strong
3. Ionic compounds are soluble in water
4. Ionic compounds will have large electronegative difference

Question 27

Which force is the only one which acts on non-polar and monatomic molecules?

Answer 27

LDF’s

Question 28

When does hydrogen bonding occur?

Answer 28

Between polar molecules where an H is directly bonded to an O, N or F

Question 29

How are LDF’s created?

Answer 29

The uneven distribution of moving electrons creates temporary dipoles

Question 30

Induced dipole?

Answer 30

Dipole of an atom caused by it’s neighbour

Question 31

List the strength of each type of bonding from weakest to strongest

Answer 31

LDF’s, permanent dipole-dipole, hydrogen bonding, covalent molecular, ionic, covalent network

Question 32

In terms of LDF’s, the larger the atoms…

Answer 32

…the stronger the LDF’s and subsequently its mp and bp are higher

Question 33

Generally, how can viscosity be increased?

Answer 33

By increasing the number of OH groups

Question 34

Why is ice less dense than water?

Answer 34

The most efficient hydrogen bonding in ice is an ‘open lattice’ which results in lots of space between molecules