3.2 Physical Chemistry (completed)

Question 1

What is an exothermic reaction?

Answer 1

Energy is given out for example combustion of fuels, respiration

-tve enthalpy change

Question 2

What is an endothermic reaction?

Answer 2

Energy is absorbed for example photosynthesis, thermal decomposition

+ tve enthalpy change

Question 3

What is the equation for enthalpy change?

Answer 3

Products - reactants

Question 4

What is the definition of activation energy in terms of bonds?

Answer 4

The energy needed to start a reaction by breaking chemical bonds in the reactants

Question 5

What is the bond dissociation energy?

Answer 5

The energy released when a bond is formed

Question 6

What is the average bond enthalpy?

Answer 6

The breaking of one mole of bonds in gaseous molecules

Question 7

What is the equation for enthalpy change in terms of bonds?

Answer 7

Bonds broken - bonds formed

Question 8

What are the problems with bond enthalpy calculations?

Answer 8

They always assume substances are in the gaseous state

Mean bond energy values are used

Question 9

What is calorimetry?

Answer 9

A way to determine the enthalpy change of a reaction

Question 10

What is the equation for enthalpy change from calorimetry?

Answer 10

q = mcΔT

Then divide by moles and 1000

Question 11

What is the method of spirit burner calorimetry?

Answer 11

A known volume of cold water is measured into the beaker
The starting temperature of the water is recorded
The water is heated using the flame from the burning fuel
The final temperature of the water is recorded
The spirit burner containing the fuel is weighed before and after the experiment 

Question 12

What is the enthalpy of reaction?

Answer 12

The overall energy change

Question 13

If the conditions are standard then what is the energy change?

Answer 13

Standard enthalpy of reaction

Question 14

What are the standard conditions?

Answer 14

100kPa 1atm
298K
1.0 M

Question 15

What is the standard enthalpy change of combustion?

Answer 15

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 state

Question 16

What is the standard enthalpy change of formation?

Answer 16

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 Hess’ law?

Answer 17

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

Question 18

What is enthalpy change of combustion and formation equations?

Answer 18

C=R-P
F=P-R

Always use equation of data given

Question 19

What must happen for a reaction to occur?

Answer 19

Particles must collide

Question 20

What are the five factors that affect rate of reaction?

Answer 20

Temperature
Pressure 
Catalyst
Concentration 
Surface Area

Question 21

What is the activation energy?

Answer 21

The minimum amount of energy for particles to react when they collide

Question 22

What happens if particles collide but don’t have activation energy?

Answer 22

They bounce off of each other

Question 23

What does a Maxwell-Boltzmann distribution look like?

Answer 23

Number of molecules y axis
Kinetic Energy x axis
Bell shaped from origin that never reaches x axis
Area under graph represents the total number of molecules

Question 24

How does a Maxwell Boltzmann distribution change when temperature is increased?

Answer 24

The peak gets lower and the curve gets broader

Question 25

How does increasing temperature affect the rate of reaction?

Answer 25

Increases

Increasing temperature it gives particles more energy so more of them have enough energy to react when they collide

Question 26

Is the definition of a catalyst?

Answer 26

Substances which increase the rate of a chemical reaction without being consumed themselves by providing an alternative route for the reaction with a lower activation energy

Question 27

What are the benefits and negative effects of catalysts?

Answer 27

Advantages:
Increased sustainability
Lower operating temperature
Less CO2 emissions by burning fossil fuels

Disadvantages:
Toxicity

Question 28

What are the two types of catalysis?

Answer 28

Homogenous Catalysis
Catalysts and reactants are in the same phase

Heterogenous Catalysis
Catalysts and reactants are in different phases

Question 29

What is Le Chatelier’s principle?

Answer 29

When a system in dynamic equilibrium is subject to change the system will adjust to minimise change

Question 30

What are the five characteristics of a dynamic equilibrium?

Answer 30

1. Rate of forward reaction equals rate of reverse
2. Occurs in a closed system
3. Concentrations of reactants and products remain constant
4. Reactions to continue to occur as the reaction is dynamic
5. The equilibrium can be established from either side

Question 31

What are the advantages and disadvantages for high pressure and high temperature?

Answer 31

Increase rate and possibly increased yield
BUT
Costs for energy and equipment needed and also possibly unsafe

Question 32

What are the advantages and disadvantages for low pressure and low temperature?

Answer 32

Reduce costs and possibly increase yield
BUT
Decrease rate

Question 33

Where will an equilibriums shift if you increase temperature and pressure?

Answer 33

Favours endothermic and reaction that produces less moles

Question 34

How do catalysts affect equilibrium position?

Answer 34

No effect