Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry > Chapter 22 - enthalpy and entropy > Flashcards

Chapter 22 - enthalpy and entropy Flashcards

1
Q

Define lattice enthalpy

A

The enthalpy change that accompanies the formation of 1 mole of an ionic lattice from its gaseous ion`s under standard conditions of 298K and 100kPa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define standard enthalpy change of formation

A

The enthalpy change that takes place when 1 mole of a compound is formed from its elements under standard conditions of 100kPa and 298K with each element in their standard states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define standard enthalpy change of atomisation

A

The enthalpy change that takes place for the formation of 1 mole of an element in gaseous form from the element in its standard state under standard conditions of 100kPa and 298K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Define first ionisation energy

A

The energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define first electron affinity

A

The energy change that takes place when 1 electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Define second ionisation energy

A

The enthalpy change required to remove 1 electron from each ion in 1 mole of 1+ ions to form 1 mole of 2+ ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Define second electron affinity

A

The enthalpy change that occurs when 1 electron is added to each ion in 1 mole of gaseous 1- ions to form 1 mole of gaseous 2- ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Is lattice enthalpy endothermic or exothermic? Why?

A

Exothermic because energy is given out when ionic bonds are formed from gaseous ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Is the standard enthalpy change of atomisation endothermic or exothermic? Why?

A

Endothermic because bonds are broken to form gaseous atoms which requires energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Is the standard enthalpy change of formation endothermic or exothermic?

A

It can be either but it is usually exothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Is first ionisation energy endothermic or exothermic? Why?

A

Endothermic because the electron being lost has to overcome attraction from the nucleus in order to leave the atom which requires energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Is second ionisation energy endothermic or exothermic? Why?

A

Endothermic because the electron being lost has to overcome attraction from the nucleus in order to leave the atom which requires energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Is first electron affinity endothermic or exothermic? Why?

A

Exothermic because the electron is being attracted into the outer shell of an atom by the nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Is second electron affinity endothermic or exothermic? Why?

A

Endothermic because the electron is repelled by the 1- ions which has to be overcome which requires energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does lattice enthalpy indicate?

A

The strength of an ionic lattice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does lattice enthalpy measure?

A

A measure of how strong an ionic bond is in a giant ionic lattice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a Born - Haber cycle?

A

An energy diagram used to calculate lattice enthalpies by taking an indirect route

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

List 2 factors that affect lattice enthalpy

A

size of ions

ionic charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Explain how ionic charge influences lattice enthalpy

A

Across a period, ionic charge increases, meaning attraction between ions increases, and lattice enthalpy becomes more exothermic, as ionic bonds are stronger between the oppositely charged ions, and thus lattice enthalpy is increased

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Explain how size of ions influences lattice enthalpy

A

Ionic size increases down a group
And the distance between ions in lattice increases as there are more shells
Therefore, the attraction between the ions decreases
And lattice enthalpy becomes less exothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

The more negative the lattice enthalpy the ____ the melting point

A

Higher

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Define enthalpy change of solution

A

The enthalpy change that takes place when 1 mole of a solute dissolves in a solvent under standard conditions of 298K and 100kPa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Give an equation showing enthalpy change of a solution

A

NaCl (s) + aq –> Na+ (aq) + Cl- (aq)

24
Q

Give the experimental procedure to calculate enthalpy change of solution

A
  1. Weigh out sample using mass balance
  2. Measure out known volume of water using a measuring cylinder
  3. Measure the temperature of water using a thermometer
  4. Stir the mixture using the thermometer until all has dissolved and temperature no longer changes. Record this value
  5. Use q=mc. T to calculate energy in j
  6. Use enthalpy change of solution =(q/1000 - needs to be in kJmol-1) /n to calculate enthalpy change, where n = moles and q= energy
25
Q

What are the stages of dissolving a solute in water?

A

The ionic lattice is broken down into gaseous ions

The ions then become hydrated so the ions bond with water molecules

26
Q

Define enthalpy change of hydration

A

The enthalpy change that takes place when gaseous ions are dissolved in water to form 1 mole of aqueous ions under standard conditions of 298K and 100kPa

27
Q

List 2 factors affecting enthalpy of hydration

A

size of ions

ionic charge

28
Q

Explain how size of ions affects enthalpy change of hydration

A

Distance between ions increases as ionic size increases
Therefore, the attraction between the ions and water molecules decreases
And hydration enthalpy becomes less exothermic

29
Q

Explain how ionic charge of the enthalpy change of hydration

A

The attraction between ions and water molecules increases as ionic charge increases
Hydration enthalpy therefore becomes more exothermic

30
Q

What is entropy?

A

A measure of how dispersed energy is within a system

31
Q

What does it mean when entropy is greater?

A

The dispersal of energy and the disorder of the molecules is greater

32
Q

Does entropy increase or decrease over time?

A

increase, as energy will disperse over time

33
Q

What are the units of entropy?

A

JK-1mol-1

34
Q

Which has the greatest entropy? Solids, liquids or gases

A

gases, as they have the greatest dispersal of energy

35
Q

At 0K how much entropy do perfect crystals have?

A

zero entropy

36
Q

When a system changes, if the energy becomes —– then the entropy will increase, and the entropy change is —

A

more dispersed

positive

37
Q

When a system changes, if the energy becomes —–then the entropy will decrease, and the entropy change is —–.

A

less dispersed/ more concentrated

negative

38
Q

List 4 instances when entropy in a system increases

A

Melting
Boiling
Number of gaseous molecules increases
Dissolving a substance

39
Q

Define standard entropy

A

the entropy of 1 mole of a substance under standard conditions of 100kPa and 298K

40
Q

Give the equation to calculate entropy change in a system

A

Entropy change = the sum of the entropy of the products – the sum of the entropy of the reactants

41
Q

What does it mean for a reaction to be feasible?

A

It will occur spontaneously

42
Q

When is a reaction feasible (in terms of energy change)

A

A chemical system becomes more stable and its overall energy decreases

43
Q

What is overall energy of a system known as?

A

Free energy change

44
Q

What does the Gibbs equation calculate?

A

The equation to calculate free energy change

45
Q

What is the Gibbs equation (give formula)

A

Free energy change Jmol-1 = enthalpy change kJmol-1 – entropy change at a specific temperature

46
Q

How do you calculate entropy change at a specific temperature?

A

(temperature K x entropy change JK-1mol-1)

47
Q

How do you convert from celcius to kelvin?`

A

ADD 273

48
Q

For a reaction to be feasible the free energy change has to be less than ___

A

zero

49
Q

If the enthalpy change is negative and entropy change is positive will the reaction be feasible?

A

Yes, because the free energy change is less than zero. -10 - +10 = -20

Remember, you are subtracting entropy, so if it is positive, a negative sign and a positive sign make a negative

50
Q

If the enthalpy change is positive and the entropy change is negative will the reaction be feasible? why?

A

No, because free energy change will always be more than 0

10 - - 10 = 20

Remember, you are subtracting entropy, and a negative sign and negative sign make a positive

51
Q

What other factors need to be considered when considering if a reaction will occur?

A

activation energy

rate of reaction

52
Q

If the enthalpy change is negative and the entropy is negative, what conditions are needed in order for the reaction to be feasible? Why?

A

Low temperatures are needed, so that T^S is smaller than enthalpy

-10 –7 = -3

53
Q

If the enthalpy change is positive and the entropy is positive what conditions are needed in order for the reaction to be feasible? Why?

A

High temperatures are needed, so that T^S is bigger than enthalpy, so that the overall reaction is negative

10 - +17 = -7

54
Q

What is the enthalpy change of an endothermic reaction?

A

Positive

55
Q

What is the enthalpy change of an exothermic reaction?

A

Negative

56
Q

In order for an endothermic reaction to be feasible, what conditions are there?

A

T^S must be positive, and must be larger than ^H, so temperatures must be high so that the overall reaction is negative

10 - +17 = -7

  • this makes sense with Le Chatelier so double check answers
57
Q

In order for an exothermic reaction to be feasible, what conditions are there?

A

T^S must either be positive, or more less negative than ^H, so that the overall energy change is still negative.

Either

-10 - + 7 = -17
or
-10 - - 3 = -7

Chemistry (21 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions