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Energetics Flashcards

1
Q

Why do enthalpy changes take place?

A

Bonds are being broken or formed during a reaction

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2
Q

What is needed to overcome attractive forces between atoms?

A

Energy in form of heat

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3
Q

Is bond breaking endothermic or exothermic?

A

Endothermic

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4
Q

Is bond forming endothermic or exothermic?

A

Exothermic

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5
Q

What does endothermic mean?

A

A chemical reaction that absorbs heat from its surroundings

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6
Q

What does exothermic mean?

A

A chemical reaction that releases heat into its surroundings

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7
Q

What determines if the overall reaction is endothermic or exothermic?

A

The sum of energy in and out

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8
Q

When is the overall reaction endothermic?

A

If more energy is required to break bonds than energy released when new bonds form

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9
Q

When is the overall reaction exothermic?

A

If more energy is released when new bonds form than energy required to break bonds

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10
Q

What is an energy level diagram?

A

A diagram that shows energies of reactants, transition states and products as reaction proceeds

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11
Q

What is meant by transition state?

A

Stage during reaction at which chemical bonds are partially broken and formed

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12
Q

What is needed to reach the transition state?

A

Activation energy (Ea)

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13
Q

What is meant by activation energy?

A

The minimum amount of energy needed for reactant molecules to successfully collide and start a reaction

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14
Q

Whats higher in energy in an exothermic reaction?

A

The reactants are higher in energy that the products

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15
Q

Which reactions have a lower activation energy exothermic or endothermic? Why?

A

Exothermic become the reactants are closer in energy to the transition state

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16
Q

Whats higher in energy in an endothermic reaction?

A

The products are higher in energy than the reactants

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17
Q

What is meant by enthalpy?

A

The total chemical energy inside a substance

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18
Q

What symbol represents enthalpy change?

A

ΔH

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19
Q

Is enthalpy change positive or negative?

A

Can be either

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20
Q

What results are seen by an exothermic reaction?

A

Increased temperature of surroundings
Decreased energy of system

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21
Q

What results are seen by an endothermic reaction?

A

Decreased temperature of environment
Increased energy of system

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22
Q

What ΔH do exothermic reactions have?

A

Negative

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23
Q

What ΔH do endothermic reactions have?

A

Positive

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24
Q

Describe standard conditions.

A

A pressure of 100 kPa
A temperature of 298 K
A concentration of 1 mole
Each substance involved in its standard physical state

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25
What allows for the comparison of enthalpy?
All measurements are carried out under standard conditions
26
What symbol is used to show reaction was carried out under standard conditions?
Ꝋ
27
What is meant by the standard enthalpy change of reaction?
The enthalpy change when the reactants in the strochiometric equation react to give the products under standard conditions
28
What symbol is used to represent the standard enthalpy change of reaction?
ΔHᵒᵣ
29
What is meant by the standard enthalpy change of formation?
The enthalpy change when one mole of a compound is formed from its elements under standard conditions
30
What symbol is used to represent the standard enthalpy change of formation?
ΔHᵒf
31
What is meant by the standard enthalpy change of combustion?
The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions
32
What symbol is used to represent the standard enthalpy change of combustion?
ΔHᵒ꜀
33
What is meant by the standard enthalpy of neutralisation?
The enthalpy change when one mole of water is formed by reacting an acid and alkali under standard conditions
34
What symbol is used to represent the standard enthalpy change of neutralisation?
ΔHᵒₙₑᵤₜ
35
Is the standard enthalpy change of reaction endothermic or exothermic?
Both
36
Is the standard enthalpy change of formation endothermic or exothermic?
Both
37
Is the standard enthalpy change of combustion endothermic or exothermic?
Exothermic
38
Is the standard enthalpy change of neutralisation endothermic or exothermic?
Exothermic
39
What is the standard enthalpy change of formation of an element in its standard state?
Zero
40
What is calorimetry?
The measurement of enthalpy changes in chemical reactions
41
What can be used as a simple calorimeter?
Polystyrene cup Vacuum flask Metal can
42
What is specific heat capacity?
The energy needed to increase the temperature of 1g of a substance by 1ᵒC
43
What is the specific heat capacity of water?
4.18 J g⁻¹ ᵒC⁻¹
44
How can energy transfer in calorimetry be calculated?
q = m x c x ΔT
45
What does q represent in q = m x c x ΔT?
Heat transfer
46
What is q measured in in q = m x c x ΔT
Joules (J)
47
What does m represent in q = m x c x ΔT?
Mass of water
48
What is m measured in in q = m x c x ΔT?
Grams (g)
49
What does c represent in q = m x c x ΔT?
Specific heat capacity
50
What is c measured in in q = m x c x ΔT?
J g⁻¹ ᵒC⁻¹
51
What does ΔT represent in q = m x c x ΔT?
Temperature change
52
What is ΔT measured in in q = m x c x ΔT?
ᵒC
53
What are enthalpy cycles used for?
Finding average bond energy as bond energies cannot be found directly
54
What is the enthalpy change of atomisation?
The enthalpy change when one mole of gaseous atoms is formed from its elements under standard conditions
55
What symbol is used to represent the enthalpy change of atomisation?
ΔHᵒₐₜ
56
What is bond dissociation energy?
The amount of energy required to break one mole of a specific covalent bond in the gas phase
57
What other names are given to bond dissocation energy?
Bond energy Bond enthalpy
58
What symbol is used to represent bond enthalpy?
E( )
59
What are bond energies affected by?
Other atoms in environment
60
What is used to calculate average bond energy?
Number of same types of bond in different environments
61
How can bond energies be used to find the enthalpy change of reaction?
ΔHᵒᵣ = enthalpy change for bonds broken + enthalpy change for bonds formed
62

Save My Exams - Chem (19 decks)

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