energetics

Question 1

what are the standard conditions?

Answer 1

298K, 1 bar and 1moldm^-3

Question 2

what is the enthalpy change of reaction?

Answer 2

it is the energy change of a given stoichiometric equation at the given temperature and pressure

Question 3

what is the standard enthalpy change of formation?

Answer 3

it is the energy change when one mole of a substance is formed from its constituent elements in their standard states at 298K and 1 bar

Question 4

what is the standard enthalpy change of combustion?

Answer 4

it is the energy that evolved when one mole of a substance is burnt completely in excess oxygen at 298K and 1 bar.

Question 5

what is the standard enthalpy change of neutralisation?

Answer 5

it is the energy evolved when one mole of water is formed in the reaction between an acid and an alkali at 298K and 1 bar

Question 6

what is the standard enthalpy change of atomisation?

Answer 6

it is the energy absorbed when one mole of gaseous atoms is formed from the element at its standard state at 298K and 1 bar.

Question 7

what is bond energy?

Answer 7

it is the average energy absorbed when one mole of a given covalent bond in a gaseous compound is broken into gaseous atoms

Question 8

what is lattice energy?

Answer 8

it is the energy evolved when one mole of an ionic solid is formed from its constituent gaseous ions

Question 9

what is the standard enthalpy change of hydration?

Answer 9

it is the energy that evolved when one mole of gaseous ions is converted to one mole of aqueous ions at infinite dilution at 298K and 1 bar.

Question 10

what is the standard enthalpy change of solution?

Answer 10

it is the energy change when one mole of a substance is completely dissolved in infinite dilution in an aqueous solution at 298K and 1 bar

Question 11

what is the first electron affinity?

Answer 11

it is the energy change when one mole of gaseous atoms of an element gain one mole of electrons to form one more of singly charged negative gaseous ions.

Question 12

to determine heat change of a reaction conducted in the calorimeter…

Answer 12

we use the equation q = mc(del)T

Question 13

what are the assumptions applied to determine heat change of a reaction?

Answer 13

1. there is no heat lost to the surroundings
2. the heat capacity of the solution is approx. to that of water and has a value of 4.18Jg^-1K^-1
3. the density of the solution is approx. to that of water and has a value of 1gcm^-3

Question 14

the enthalpy change of a reaction can be determined using…

Answer 14

q/n

Question 15

what is hess’ law?

Answer 15

it states that the enthalpy change for a reaction is the same whether the reaction takes place in one step or in a series of steps and is determined by the initial and final states of the system

Question 16

define entropy

Answer 16

it is the measure of the randomness or the disorder in a system

Question 17

what does a positive entropy value mean?

Answer 17

the final state is more disordered than its initial state

Question 18

what does a negative entropy value mean?

Answer 18

the final state is less disordered than its initial state

Question 19

how does temperature affect entropy?

Answer 19

entropy increases when temperature increases as there are more ways of arrangement for the particles and there is a broadening of the energy distribution, leading to more energy states which the particles can adopt.

Question 20

how does the change in the number of particles affect entropy?

Answer 20

it increases as there is an increase in the number of ways to arrange the particles.

Question 21

how does mixing the particles increase entropy?

Answer 21

there are more ways to arrange the particles after mixing.

Question 22

what is the standard gibbs free energy change equation?

Answer 22

change in standard gibbs free energy = standard enthalpy change of the system - temperature*standard entropy change of the system

Question 23

if change in standards gibbs free energy > 0…

Answer 23

the chemical reaction is spontaneous

Question 24

if change in standards gibbs free energy < 0…

Answer 24

the chemical reaction is NOT spontaneous

Question 25

what are the limitations of the use of “change in standard gibbs free energy”?

Answer 25

thermodynamic feasibility does not predict the kinetics of a reaction, such as its rate and the reaction may not take place because of a high activiation energy barrier