Chemistry - Chains, Energy and Resources - F322 - Energy (3)

Question 1

Define chemical energy.

Answer 1

Chemical energy is a special form of potential energy that lies within chemical bonds.

Question 2

Define ethalpy, H.

Answer 2

Ethalpy, H, is the heat content that is stored in a chemical system.

Question 3

Define exothermic.

Answer 3

Exothermic refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (ΔH-ve)

Question 4

Define endothermic.

Answer 4

Endothermic refers to a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken from the surroundings (ΔH+ve)

Question 5

What is probably the most important exothermic reaction for life?

Answer 5

Respiration is probably the most important exothermic reaction for life.

Question 6

What is probably the most important endothermic reaction for life?

Answer 6

Photosynthesis is probably the most important endothermic reaction for life.

Question 7

Define the activation energy.

Answer 7

Activation energy is the minimum energy required to start a reaction by the breaking of bonds.

Question 8

Once an exothermic reaction begins, what is regenerated making the reaction self-sustaining?

Answer 8

Once an exothermic reaction begins, the activation energy is regenerated and the reaction becomes self-sustaining.

Question 9

What is the standard conditions of pressure?

Answer 9

Standard pressure is 100kPa (1 atmosphere)

Question 10

What is the standard conditions of temperature?

Answer 10

Standard temperature is 25oC or 298K

Question 11

What is the standard conditions of concentration?

Answer 11

Standard concentration is 1.0moldm-3 (for reactions with aqueous solutions).

Question 12

What is the symbol for standard enthalpy change?

Answer 12

ΔHθ is the symbol for standard enthalpy change.

Question 13

Define the standard state.

Answer 13

The standard state is the physical state of a substance under standard conditions of 100kPa and 298K

Question 14

Define the standard enthalpy change of reaction, ΔHCθ

Answer 14

The standard enthalpy change of reaction, ΔHθC is the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in standard states

Question 15

Define the standard enthalpy change of combustion, ΔHθ

Answer 15

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

Question 16

Define the enthalpy change of formation, ΔHfθ

Answer 16

The standard enthalpy change of formation, ΔHfθ, of a compound is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 17

What is the standard enthalpy change of formation of an element?

Answer 17

The standard enthalpy change of an element is defined as 0kJmol-1

Question 18

What equations determines the heat exchange with the surroundings?

Answer 18

Q=mcΔT joules.
Where m is the mass of the surroundings
c is the specific heat capacity of the surroundings
ΔT is the temperature change of the surroundings

Question 19

Define the specific heat capacity.

Answer 19

Specific heat capacity, c, is the energy required to raise the temperature of 1g of a substance by 1oC

Question 20

Is the breaking of bonds endothermic or exothermic?

Answer 20

Breaking of bonds is endothermic, energy is required to break them.

Question 21

Is the formation of bonds endothermic or exothermic?

Answer 21

The formation of new bonds is exothermic, energy is released.

Question 22

In an exothermic reaction, are the bonds formed stronger or weaker than the ones broken?

Answer 22

In an exothermic reaction, the bonds that are formed are stronger than the bonds that are broken.

Question 23

In an endothermic reaction, are the bonds formed stronger or weaker than the ones broken?

Answer 23

In an endothermic reaction the bonds that are formed are weaker than the bonds that are broken.

Question 24

Why is it not always possible to measure the enthalpy change of reaction directly?

Answer 24

• a high activation energy
• slow reaction rate
• more than one reaction taking place

Question 25

What does Hess’ Law state?

Answer 25

Hess’ law states that if 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.

Question 26

The rate of a chemical reaction can often be altered by…?

Answer 26

• temperature
• pressure, where the reactants are gases
• concentration
• surface area
• adding a catalyst

Question 27

What does collision theory state?

Answer 27

Collision theory states that a chemical reaction will only take place when the reactants collide, the required activation energy is met and the molecules are in the correct orientation.

Question 28

How does increasing the reactants affect the rate of reaction?

Answer 28

Increasing the concentration of reactants increases the rate of reaction

Question 29

How does increasing the pressure affect the rate of reaction?

Answer 29

Increasing the pressure increases the rate of reaction because the same number of molecules occupies a smaller space, which leads to more collisions.

Question 30

What is used as the catalyst in the Haber process?

Answer 30

Iron is used as the catalyst for the Haber process.

Question 31

What is used as the catalyst in the contact process?

Answer 31

V2O5 is used as the catalyst in the contact process.

Question 32

What is used as the catalyst in the hydrogenation of margarine?

Answer 32

Nickel is used as the catalyst in the hydrogenation of margarine.

Question 33

How do catalytic converters improve air quality?

Answer 33

Catalytic converters improve air quality by reducing toxic emissions from vehicles and preventing photochemical smog.

Question 34

Define heterogeneous catalysis.

Answer 34

Heterogeneous catalysis is catalysis of a reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases whilst catalysts are solids.

Question 35

Define homogeneous catalysis.

Answer 35

Homogeneous catalysis is catalysis of a reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state.

Question 36

What is biocatalysis?

Answer 36

Biocatalysis is catalysis where the catalyst is an enzyme.

Question 37

How does the industrial use of enzymes have benefits?

Answer 37

• lower temperatures and pressures can be used than with inorganic catalysts
• enzymes often allow a reaction to take place that forms pure products
• conventional catalysts are often poisonous, enzymes are biodegradeable

Question 38

In a Boltzmann distribution, what is the area under the graph equal to?

Answer 38

In a Boltzmann distribution, the area under the graph is equal to the total number of molecules in the sample

Question 39

What happens to a Boltzmann distribution under increased temperature?

Answer 39

With increasing temperature, the distribution flattens and shifts to the right.

Question 40

Define dynamic equilibrium.

Answer 40

Dynamic equilibrium is the equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.

Question 41

What does le Chatelier’s principle state?

Answer 41

le Chatelier’s principle states that when a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to minimise the change.