L1 - Chemical Reactivity

Question 1

Define ‘energy’.

Answer 1

The ability to do work.

Question 2

Define ‘work’.

Answer 2

The distance moved against an opposing force.

Question 3

What is the equation for work?

Answer 3

Work = Force x Distance

Question 4

What units is energy measured in?

Answer 4

Joules (J)

Question 5

Define ‘1 Joule’.

Answer 5

The amount of energy required to raise a 1kg substance 10cm against the force of gravity.

Question 6

Define ‘1 Calorie’.

Answer 6

The amount of heat necessary to raise the temperature of exactly one gram of water by one degree Celsius.

Question 7

What are the conversions into kcal and cal for 1 calorie.

Answer 7

1 calorie = 1 kcal = 1000 cal

Question 8

Describe potential energy.

Answer 8

• Stored energy

- Energy due to position

Question 9

What is the equation for potential energy?

Answer 9

PE = mgh

Question 10

Describe kinetic energy.

Answer 10

• Energy of motion

- Depends on mass and velocity

Question 11

What is the equation for kinetic energy?

Answer 11

KE = 1/2mv^2

Question 12

Describe chemical energy.

Answer 12

• Energy stored in bonds

Question 13

State the 5 different types of energy.

Answer 13

• Potential energy
• Kinetic energy
• Electromagnetic energy
• Nuclear energy
• Chemical energy

Question 14

State the ‘First Law of Thermodynamics’ / Law of Conservation of Energy.

Answer 14

“Energy cannot be created or destroyed by any physical and chemical changes - it can only be converted from one form to another.”

Question 15

What are the conditions for chemical reactions to occur?

Answer 15

• Reactants energetic

- Reactants oriented correctly

Question 16

Energy is either ________ or ________.

Answer 16

Energy is either released or absorbed.

Question 17

What is the change in energy?

Answer 17

The difference between bond energies of reactants and products.

Enthalpy change of reaction (ΔH)

Question 18

Define ‘enthalpy’.

Answer 18

A measure of the heat content of a substance at constant pressure.

Question 19

What does ΔH° mean?

Answer 19

Heat released / absorbed during a chemical reaction at standard conditions

Question 20

What is the equation for ΔH°?

Answer 20

ΔH° = H.products - H.reactants

Question 21

What can you not measure?

Answer 21

Cannot measure the actual enthalpy of a substance (but can measure enthalpy change)

Question 22

What is the standard state of an element?

Answer 22

• 1 atmosphere

- 25°C

Question 23

What is the standard state of a compound?

Answer 23

• Gaseous substance = 1 atmosphere
• Pure substance in a condensed state (liquid / solid) = state it would have at 1 atmosphere
• Substance in solution = concentration of 1M

Question 24

What is used to indicate physical state?

Answer 24

Subscripts:

• (g)
• (l)
• (s)

Question 25

Describe the 3 characteristics of exothermic reactions.

Answer 25

- Negative ΔH - Heat given out - Enthalpy of reactants > products

Question 26

Describe the 3 characteristics of endothermic reactions.

Answer 26

- Positive ΔH - Heat absorbed - Enthalpy of products > reactants

Question 27

What will happen to the temperature of an exothermic reaction?

Answer 27

Temperature of the system will be observed to rise.

Question 28

What will happen to the temperature of an endothermic reaction?

Answer 28

Temperature of the system will fall (in practice, reactants will be heated to speed up the reaction and provide the absorbed heat).

Question 29

What happens during bond breaking?

Answer 29

Energy is added

Question 30

What happens during bond making?

Answer 30

Energy is released

Question 31

Define 'entropy'.

Answer 31

Measures the amount of energetic disorder in a system.

Question 32

When is entropy higher?

Answer 32

When the disorder / randomness of particles in a substance / mixture are greater.

Question 33

What is the symbol of entropy?

Answer 33

S

Question 34

What units is entropy measured in?

Answer 34

J mol^-1 K^-1

Question 35

What is the equation for ΔS?

Answer 35

ΔS = S.final - S.initial

Question 36

What is the equation for ΔS.total?

Answer 36

ΔS.total = ΔS.system + ΔS.surroundings

Question 37

State the 'Second Law of Thermodynamics'.

Answer 37

"Entropy tends to a maximum."

Question 38

What do all spontaneously occurring chemical and physical changes involve?

Answer 38

An overall increase in entropy.

Question 39

Describe scenarios in which entropy is increased.

Answer 39

- Solids melting - Liquids boiling - Number of molecules increasing - Ionic solids dissolving - Temperature increasing

Question 40

Define 'Gibbs Free Energy'.

Answer 40

Energy from a reaction free to do work.

Question 41

What is the equation for ΔG?

Answer 41

ΔG = ΔH - TΔS

Question 42

What happens if ΔG < 0?

Answer 42

Reaction will be spontaneous

Question 43

What happens if ΔG > 0?

Answer 43

Reaction needs energy input to occur

Question 44

What happens if ΔG = 0?

Answer 44

System is in equilibrium

Question 45

What is the quantity of ΔG if the reaction is spontaneous?

Answer 45

ΔG < 0

Question 46

What is the quantity of ΔG if the reaction needs energy input to occur?

Answer 46

ΔG > 0

Question 47

What is the quantity of ΔG if the system is in equilibrium?

Answer 47

ΔG = 0

Question 48

What happens during catabolic reactions?

Answer 48

High energy compounds → Simple molecules

Question 49

What happens during anabolic reactions?

Answer 49

Simple subunit → Complex molecule

Question 50

How do anabolic reactions take place?

Answer 50

In steps, coupled with ATP hydrolysis or another exergonic reaction.

Question 51

State the ΔG of the following reaction: glucose + 6O2 → 6CO2 + 6H2O

Answer 51

ΔG = -2870 kJ mol^-1

Question 52

State the ΔG of the following reaction: ATP + H2O → ADP + Pi

Answer 52

ΔG = -30.5 kJ mol^-1

Question 53

State the ΔG of the following reaction: glucose + fructose → sucrose

Answer 53

ΔG = +29.3 kJ mol^-1

Question 54

State the ΔG of the following reaction: glucose + ATP → glucose,p + ADP

Answer 54

ΔG = -16.7 kJ mol^-1

Question 55

State the ΔG of the following reaction: fructose + ATP → fructose,p + ADP

Answer 55

ΔG = -14.2 kJ mol^-1

Question 56

State the ΔG of the following reaction: glucose,p + fructose,p → sucrose + 2Pi

Answer 56

ΔG = -0.8 kJ mol^-1