DEFINITIONS

Question 1

Give the meaning of the term electronegativity.

Answer 1

Power of an atom to attract a pair of electrons in a covalent bond.

Question 2

State the meaning of the term periodicity

Answer 2

Repeating pattern/trends (of physical or chemical properties/reactions)

Question 3

Explain what is meant by the term stereoisomers.

Answer 3

:compounds with the same structural formula but different arrangement of atoms in space

Question 4

Define the mass number of an atom.

Answer 4

Number of protons + neutrons

Question 5

State the meaning of the term atomic number

Answer 5

The atomic number (i.e. proton number), Z is equal to the number of protons.

Question 6

State the meaning of the term isotope

Answer 6

Isotopes are atoms with the same number of protons but a different
number of neutrons.

Question 7

State the meaning of the term ionisation

Answer 7

amount of energy needed to remove a mole of electrons from a mole of atoms, in the gaseous state.

Question 8

State the meaning of the term Relative Atomic Mass - Ar

Answer 8

Relative Atomic Mass (Ar) = Average mass of one atom of an element / 1/12th the mass of a C12 atom

Question 9

State the meaning of the term Relative Molecular Mass - Mr

Answer 9

Relative Molecular Mass (Mr) = Average mass of one molecule compared to 1/12th the mass of a C12 atom

Question 10

State the meaning of the term Empirical formula

Answer 10

simplest whole number ratio of atoms of each element.

Question 11

State the meaning of the term Molecular Formulae

Answer 11

the actual number of atoms of each element.

Question 12

Definition of The Avogadro Constant

Answer 12

The Avogadro Constant is the number of atoms in 12g of C12

Question 13

Definition of a Nucleophile

Answer 13

• An electron-pair donor

Question 14

What is a positive inductive effect?

Answer 14

The ability to release electron density through a covalent bond

Question 15

Definition of Structural Isomerism

Answer 15

Structural isomers have the same molecular formula but different structural formula.

Question 16

What is mass spectrometry

Answer 16

A machine that can be used to analyse elements or compounds, it accurately determines atomic mass or relative molecular mass

Question 17

Define percentage yield

Answer 17

The percentage of product produced by a reaction compared to a theoretical maximum

Question 18

Definition of reducing agent

Answer 18

(Remember is itself oxidised so OIL)
Electron donor (giving away e-)

Question 19

Define the term standard enthalpy of combustion. (3)

Answer 19

The enthalpy change when
1 mol of a compound is burned in oxygen completely substances in standard /
specified states

Question 20

State what is meant by the term hydration.

Answer 20

splitting of a molecule by the addition of water

Question 21

State what is meant by the term mean bond enthalpy.

Answer 21

Energy required) to break a given covalent bond of gaseous molecules into gaseous atoms (1) averaged over a range of compounds (1)

Question 22

define Exothermic Processes

Answer 22

Energy is released from the chemical to the surroundings during the process

The temperature of the surroundings increases

Question 23

define Endothermic Processes

Answer 23

Energy is taken in by the chemical from the surroundings during the process

The temperature of the surroundings decreases

Question 24

define Enthalpy Changes, ΔH

Answer 24

the change in heat energy at constant pressure

Question 25

define Activation Energy, Ea

Answer 25

Ea, is the minimum needed energy to start a reaction.

Question 26

define the standard enthalpy of combustion

Answer 26

· The enthalpy change when one mole of a substance

· is completely burnt in excess oxygen

· all reactants and products being in their standard states

Question 27

Question: Why may the enthalpy of combustion of a compound be difficult to measure?

Answer 27

Incomplete combustion may occur

Question 28

define Hess’ Law

Answer 28

enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products.

Question 29

Assumption made in calorimetry:

Answer 29

The energy transferred to the water from the reacting chemicals (or vice versa for endothermic reactions) is equal to the energy released (or taken in) by the reaction.

Question 30

Sources of Error in calorimetre

Answer 30

Heat loss to the surroundings
· Incomplete combustion of the fuel
· Heat energy transferred to the metal calorimeter
· Some fuel evaporates

Question 31

Improvements to Minimise Sources of Error

Answer 31

solution/solid:Add a lid – reduces heat loss
· Insulate sides of calorimeter using poylsterene – reduces heat loss
comb: Reduce distance between flame and beaker – reduces heat loss
· Put sleeve around flame to protect it from draughts

Question 32

Steps to Measure an Enthalpy Change Using a Cooling Curve

Answer 32

Record the temperature for a suitable time (3 minutes) before adding reactants together
· To establish an accurate initial temperature
· Mix reactants then record temperature every minute until a trend is seen
· Plot a graph of temperature against time
· Extrapolate the cooling curve back to the point of addition
· To establish a theoretical temperature change accounting for heat loss

Question 33

define Reducing agent

Answer 33

Electron donor

Question 34

define Oxidising agent

Answer 34

Electron acceptor

Question 35

define Redox reaction

Answer 35

Reaction involving the oxidation of one species and the reduction of another

Question 36

Definition of homogenious system

Answer 36

A homogenious system is one where all reactants and products are in the same phase.

Question 37

define Acid

Answer 37

Proton Donor

Question 38

define Base

Answer 38

Proton Acceptor

Question 39

define pH

Answer 39

pH = -Log10[H+]

Question 40

define [H+]

Answer 40

[H+] = 10-pH

Question 41

How to get pKa from Ka =

Answer 41

= -Log10Ka

Question 42

How to get Ka from pKa

Answer 42

= 10-pKa

Question 43

Kw =

Answer 43

[H+][-OH]

Question 44

Define molecular formula.

Answer 44

A formula that tells us the actual number of atoms of each different element that makes up a molecule.

Question 45

Mean bond enthalpies are always endothermic processes and have a
positive sign.
This is because energy is required to break bonds. what does a positive value indicate about strength of bond

Answer 45

The more positive the
bond enthalpy the larger the amount of energy needed to break the bond and so the stronger
the bond.

Question 46

a)State why the enthalpy of formation of Na(s) is zero.
b) State why the enthalpy of formation of liquid Na is not zero.

Answer 46

a) Na is an element
b) Na(l) is not the standard state of Na (so doesn’t have to equally 0 as in definition specifically has to be in standard condition which na is solid in sc)

Question 47

mean bond enthaply;
Give one reason why the bond enthalpy that you calculated above is
different from the mean bond enthalpy quoted in a data book.
why theoretical are different than experimental values

Answer 47

The data book value is averaged over a range of different compounds (not just
CH3CHF2 molecules).

In a real reaction the values are not mean values! Also watch out for changes of state as mean bond enthalpies
are for gases.