energy

Question 1

define standard lattice enthalpy

Answer 1

enthalpy change when 1 mole of ionic lattice is formed from its gaseous ions under standard conditions

Question 2

what is lattice enthalpy a measure of ?

Answer 2

ionic bond strength

Question 3

stronger ionic bonds have a more … lattice enthalpy

Answer 3

more negative

Question 4

explain why smaller / more charged ions have more -ve lattice enthalpy :

Answer 4

• greater charge density of the ions involved
• so stronger electrostatic attraction between ions
• more -ve lattice enthalpy

Question 5

what is Hess’s law ?

Answer 5

total enthalpy change of a reaction is always the same, no matter what route

Question 6

what is entropy a measure of ?

Answer 6

number of ways that particles can be arranged (disorder)

Question 7

the more disordered…

Answer 7

the higher the entropy is

Question 8

why do solids have a low entropy ?

Answer 8

vibrate at a fixed point – no random arrangements

Question 9

why do gases have a high entropy ?

Answer 9

constantly moving – random arrangements

Question 10

what are the factors of entropy ?

Answer 10

• physical state (gas is high)

- no. of moles (more moles is high)

Question 11

what is the symbol for entropy ?

Answer 11

S

Question 12

what are the units for entropy ?

Answer 12

J / K / mol

Question 13

delta S =

Answer 13

S of products - S of reactants

Question 14

what does feasible mean ?

Answer 14

a reaction that will occur spontaneously (without addition of energy)

Question 15

what is thermodynamically stable ?

Answer 15

when a substance reaches maximum entropy state

Question 16

what is the symbol for free energy ?

Answer 16

G

Question 17

what does delta G tell you ?

Answer 17

whether a reaction is feasible or not

Question 18

a reaction is feasible if delta G is …

Answer 18

negative

Question 19

delta G =

Answer 19

delta H - ( T x delta S)

Question 20

what are the units for free energy ?

Answer 20

J / mol

Question 21

is the reaction feasible when delta G = 0 ?

Answer 21

just feasible, so temp at which reaction becomes feasible can be worked out by rearranging the equation

Question 22

when will delta G always be +ve ?

what does it mean ?

Answer 22

delta H is +ve & delta S is -ve

not feasible

Question 23

when will delta G always be -ve ?

what does it mean ?

Answer 23

delta H is -ve & delta S is +ve

feasible

Question 24

why is a reaction not guaranteed if it is theoretically feasible ?

Answer 24

• high Ea

- very slow reaction

Question 25

what is the equation for enthalpy change ?

Answer 25

q = mc delta T

Question 26

standard enthalpy change of reaction

Answer 26

EC when reaction occurs in molar quantities same as chemical equation

Question 27

standard enthalpy change of formation

Answer 27

EC when 1 mol of a compound is formed form its elements in their standard states

Question 28

standard enthalpy change of combustion

Answer 28

EC when 1 mol of substance is completely burned in oxygen

Question 29

standard enthalpy change of neutralisation

Answer 29

EC when acid + alkali to form 1 mol of water

Question 30

soluble substances tend to have a …. enthalpy change of solution

Answer 30

exothermic (negative)

Question 31

if temp increases, what happens to E.C. of sol?

Answer 31

E.C. is -ve

- energy change