Brainscape's Knowledge GenomeTM

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


See full index

3.9 - Enthalpy > Enthalpy changes > Flashcards

Enthalpy changes Flashcards

1
Q

What is enthalpy?

A

A measure of the heat energy in a chemical system

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

What does chemical system refer to?

A

The atoms, molecules, or ions making up chemicals

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

Can enthalpy be measured?

A

No

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

Can enthalpy changes be measured?

A

Yes

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

What is enthalpy change?

A

The difference in the enthalpies of the reactants and products

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

What is the formula for enthalpy change?

A

▲H = H (products) - H (reactants)

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

What determines whether the ▲H is positive or negative?

A

Whether the products have more or less energy than the reactants

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

What does the law of conservation of energy state?

A

Energy cannot be created or destroyed

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

What happens when there is a chemical reaction involving enthalpy?

A

Heat energy is transferred between the system and the surroundings

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

What is the system?

A

The chemicals - reactants and products

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

What are the surroundings?

A

The apparatus, laboratory, and everything else not in the system

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

Why is the universe everything?

A

It includes both system and surroundings

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

How can ▲H be determined experimentally?

A

By measuring the transfer between the system and surroundings

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

What are the two types of energy transfer?

A

Exothermic and endothermic

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

What is exothermic transfer?

A

Energy is transferred from the system to the surroundings

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

What is endothermic transfer?

A

Energy is transferred from the surroundings to the system

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

What do enthalpy profile diagrams show?

A

The relative enthalpies of the reactants and products and the enthalpy change ▲H

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

What happens during an exothermic reaction?

A

The chemical system releases energy to the surroundings, increasing the temperature of the surroundings as they gain energy

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

What is the ▲H in an exothermic reaction?

A

Negative

20
Q

What happens during an endothermic reaction?

A

The chemical system takes in heat energy from the surroundings, decreasing the temperature of the surroundings as they lose energy

21
Q

What is the ▲H in an endothermic reaction?

A

Positive

22
Q

What happens during a chemical reaction?

A

Bonds in the reactants are broken by an input of energy and new bonds in the products form to complete the reaction

23
Q

What is activation energy Ea?

A

The minimum amount of energy required for a reaction to take place

24
Q

Why do reactions with small activation energies take place rapidly?

A

Energy needed to break bonds is readily available from the surroundings

25
Q

Why do reactions with large activation energies take place extremely slowly or not at all?

A

Very large activation energies present a very large energy barrier

26
Q

How is a standard physical value shown in data tables?

A

Using a special standard sign ⦵

27
Q

What does a standard enthalpy change ▲H⦵ refer to?

A

An enthalpy change under standard conditions

28
Q

What are the units for standard enthalpy change?

A

KJ mol -1

29
Q

What does mol -1 refer to?

A

The amount in mol given by the balancing numbers of the chemicals in a stated equation for the reaction

30
Q

What is standard pressure?

A

100 kPa

31
Q

What is standard temperature?

A

Usually 298K (25 oc)

32
Q

What is standard concentration?

A

1 mol dm-3

33
Q

What is standard state?

A

The physical state of a substance under standard conditions

34
Q

What is the formula for standard enthalpy change of reaction?

A

▲rH ⦵

35
Q

What is standard enthalpy change of reaction?

A

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states

36
Q

What happens when the equation is balanced with whole numbers?

A

The amounts are doubled and the enthalpy change is doubled

37
Q

What is the formula for standard enthalpy change of formation?

A

▲fH ⦵

38
Q

What is standard enthalpy change of formation?

A

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

39
Q

What does ▲fH ⦵ for an element refer to?

A

The formation of one mole of an element from its element

40
Q

What is the formula for standard enthalpy change of combustion?

A

▲cH ⦵

41
Q

What is standard enthalpy change of combustion?

A

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

42
Q

What do products become when an element reacts completely with oxygen?

A

Oxides of the elements in the substance

43
Q

What is the formula of standard enthalpy change of neutralisation?

A

▲neutH ⦵

44
Q

What is standard enthalpy change of neutralisation?

A

The energy change that accompanies the reaction of an acid by a base to form one mole of H2O (l), under standard conditions, with all reactants and products in their standard states

45
Q

Why is the value of ▲neutH ⦵ the same for all neutralisation reactions?

A

It always involves the same reaction of H+ (aq) with OH- (aq) to form one mole of H2O (l)

3.9 - Enthalpy (2 decks)

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