Brainscape's Knowledge GenomeTM

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


See full index

Chemistry module 3 > 3.2.1 Enthalpy Changes > Flashcards

3.2.1 Enthalpy Changes Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

what is the symbol for enthalpy?

A

H

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

What is enthalpy a measure of?

A

the heat energy in a chemical system

thought of as the energy stored within bonds.

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

How do you find enthalpy changes?

A

enthalpy of products - enthalpy of reactants

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

law of conservation of energy

A

energy cannot be created or destroyed only transferred

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

if energy is transferred from the system (chemicals) to the surroundings (thermometer, apparatus etc), the reaction is…

A

exothermic

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

if energy is transferred from the surroundings to the system, the reaction is…

A

endothermic

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

what is an enthalpy profile diagram?

A

a diagram for a reaction comparing enthalpy of the reactants with the products

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

if the products have a higher enthalpy than reactants, the reaction is…

A

endothermic

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

if reactants have a higher enthalpy than the products, the reaction is …

A

exothermic
the system releases energy into the surroundings and this causes a rise in temperature

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

is enthalpy change of an exothermic reaction positive or negative?

A

negative because the system releases energy into the surroundings so the products have less energy than the reactants during the progress of the reaction.

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

is enthalpy change of an endothermic reaction positive or negative and why?

A

positive because energy is transferred from the surroundings and gained by the chemical system during the progress of the reaction so the products have a higher enthalpy compared to the reactants and temperature decreases

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

what happens to temperature during an endothermic reaction?

A

decreases because energy is lost by surroundings and gained by system. The thermometer is part of the surroundings.

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

activation energy

A

the minimum energy required for a reaction to take place

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

draw a full enthalpy profile diagram for an exothermic reaction including activation energy and enthalpy change labels

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

draw a full enthalpy profile diagram for an endothermic reaction including activation energy and enthalpy change labels

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

what is standard enthalpy change?

A

enthalpy change of a reaction under standard conditions

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

What sign means standard conditions used?

A

(⦵)

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

what are the units for standard enthalpy changes?

A

kJ/mol-1

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

standard pressure

A

100kPa

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

standard concentration

A

1 moldm-3 (relevant for solutions only)

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

standard temperature

A

298K (25℃)

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

standard state

A

the physical state of a substance under standard conditions

23
Q

Standard enthalpy change of reaction (∆rH⦵)

A

the enthalpy change of a reaction in the molar quantities shown in the chemical equation under standard conditions with all reactants and products under standard conditions

24
Q

why can the standard enthalpy change of a reaction change?

A

the enthalpy change refers to a stated equation, if the balancing numbers change, eg making the balancing numbers whole by multiplying by 2, the enthalpy change will also change and multiply by 2.

25
Q

standard enthalpy change of formation ΔfH⦵

A

the enthalpy change when one mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard states

26
Q

When would you not balance the equation using whole numbers when finding the standard enthalpy of formation?

A

when more than one mole of the compound is formed because the definition for the enthalpy would not match

27
Q

what is the standard enthalpy of formation of elements ?

A

0 kJ/mol-1
forming one mole of an element from its element has no change.

28
Q

Standard enthalpy change of combustion ΔcH⦵

A

enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions with all reactants and products in their standard states

29
Q

standard enthalpy change of neutralisation ΔneutH⦵

A

enthalpy change when an acid and base react to form one mole of water under standard conditions with all reactants and products in their standard states

30
Q

why is the standard enthalpy of neutralisation value the same for all neutralisation reactions?

A

all neutralisation reaction involve H+ and OH- ions reacting to form the same one mole of water

31
Q

what is the equation used to find energy/enthalpy change?

A

q = mcΔT

32
Q

what does q stand for in the energy change equation? what are the units?

A

heat energy
Joules (J)

33
Q

what does ΔT stand for in energy change equation?

A

change in temperature measured in Kelvin (K)

34
Q

how do you convert from kelvin to degrees

A
  • 273
35
Q

specific heat capacity

A

the amount of energy required to raise the temperature of 1g of a substance by 1k

36
Q

what is the c of water?

A

4.18 J g-1 K-1

37
Q

What mass do you measure when finding energy change?

A

the mass of the material thats changing temperature - where the thermometer is

38
Q

How do you convert from J to kJ?

A

divide by 1000

39
Q

How can you determine the enthalpy change of combustion experimentally?

A

burn a liquid fuel such as methanol with a spirit burner and use this to heat a beaker of water

use this to find change in temperature of water and mass of fuel burnt. use energy change equation and find kJ/mol-1

40
Q

why might the data book values for enthalpy of combustion be different to the value obtained experimentally?

A
  • heat loss to surrounding other than water
  • incomplete combustion of methanol
  • non standard conditions
  • evaporation of methanol from the wick
41
Q

How can you find enthalpy change of a reaction experimentally ?

A

use polystyrene cups to carry out reaction as they a re waterproof, offer some insulation and use a thermometer to record temperature change

42
Q

average bond enthalpy

A

energy required to break one mole of bonds in a gaseous molecule

43
Q

why are bond enthalpies always positive ?

A

Bendomex - breaking bonds requires energy so is an endothermic process

44
Q

BENDOMEX

A

breaking bonds is endothermic making bonds is exothermic

45
Q

when the energy needed to break bonds is higher than the energy releases to make bonds, the reaction is…

A

endothermic

46
Q

when the energy releases from making bonds is higher than the energy needed to break bonds, the reaction is…

A

exothermic

47
Q

equation to find enthalpy change of a reaction from bond enthalpies

A

total bond enthalpies of reactants - total bond enthalpies of products = enthalpy change of reaction

48
Q

what are the limitations to using average bond enthalpies?

A
  • the enthalpy of a bond may be different in different conditions
  • not a standard enthalpy as average bond enthalpy needs all species in gaseous form
49
Q

Hess’ Law

A

is a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route

50
Q

How does Hess’ Law help to find enthalpy change?

A

can find enthalpy change indirectly through a different route

51
Q

enthalpy cycle

A

diagram showing different routes between reactants and products to indirectly find enthalpy change from other known enthalpy changes using Hess’ Law

52
Q

draw an enthalpy cycle for enthalpy of formation, linking reactants and products with arrows

A
53
Q

draw an enthalpy cycle for enthalpy of combustion linking reactants and products with arrows

A

Chemistry module 3 (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions