Module 3 Chapter 9

Question 1

What is enthalpy defined as

Answer 1

The total heat content within a system

Question 2

What is a chemical system

Answer 2

All the atoms, ions, and molecules that make up all the chemicals in a region of observable space

Question 3

What is enthalpy measured by

Answer 3

The heat absorbed from or released into the surroundings.

Question 4

what does the universe consist of

Answer 4

The systems and surroundings

Question 5

What is the law of conservation of energy

Answer 5

Energy is not created or destroyed. It is only transferred during the process.

Question 6

What is the heat energy released by a chemical reaction equal to

Answer 6

It is equal to the heat energy gained by the surroundings.

Question 7

What is the formula for enthalpy change

Answer 7

^H = H (products) - H (reactants)

Question 8

Because of the conservation of energy what happens to the energy

Answer 8

The change in energy has to be transferred and this transfer takes place between the system and the surroundings.

Question 9

What are examples of exothermic reactions

Answer 9

Combustion
neutralisation
Oxidation reactions
Displacement

Question 10

What is an exothermic reaction

Answer 10

A reaction that transfers energy to their surroundings and can be identified by an increase in the temperature of the surroundings.

Question 11

What is the energy transfer in an exothermic reaction

Answer 11

Energy transfer from systems to surroundings

Question 12

What are the enthalpies of the products and reactants relative to each other in an exothermic reaction and what is ^H

Answer 12

H products < H reactants
^H is negative

Question 13

What is activation energy

Answer 13

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

Question 14

What does the enthalpy profile diagram and reaction profile diagram of an exothermic reaction look like

Answer 14

DRAW IT

Question 15

What can an exothermic reaction be identified by

Answer 15

An increase in the temperature of the surroundings

Question 16

What is an endothermic reaction in terms of energy and temperature

Answer 16

A reaction that takes in energy from its surroundings and can be identified by a decrease in the temperature of the surroundings.

Question 17

What is the relative energy of the products and reactants in an endothermic reaction and what is ^H

Answer 17

H products > H reactants
^H is positive

Question 18

What does the enthalpy profile diagram and reaction profile diagram look like for an endothermic change

Answer 18

DRAW IT

Question 19

If the reaction conditions change what happens

Answer 19

The reactants and products enthalpy can change which means ^H can change as well.

Question 20

What are standard conditions

Answer 20

Standard pressure - 101kPA
Standard temperature - 298K (25 C)
Standard concentration - 1mol/dm3 (only with solutions)
Standard state - the physical state of a substance under standard conditions

Question 21

What is the symbol for when an experiment is done at standard conditions

Answer 21

DRAW IT

Question 22

What is 1 atmosphere in kPA

Answer 22

101 kPA =101,000 Pa = 1 atm

Question 23

What is enthalpy change of formation

Answer 23

The enthalpy change when 1 mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard state.

Question 24

What is the enthalpy change of formation of an element always

Answer 24

0 KJ/mol

Question 25

What is the enthalpy change of combustion

Answer 25

When 1 mol of a substance reacts with oxygen under standard conditions with all reactants and products in their standard state.

Question 26

What is enthalpy change of neutralisation

Answer 26

The enthalpy change that accompanies a reaction of an acid and base to form 1 mole of water under standard conditions with all reactants and products in their standard state.

Question 27

What is the enthalpy change for neutralisation always

Answer 27

- 57 Kj/mol

Question 28

What is the equation to find the heat energy in a temperature change

Answer 28

^q = m x c x t Heat energy (j) = mass (g) x specific heat capacity (J/gk) x temperature change (K)

Question 29

What can you use to dirt mine the enthalpy change of combustion

Answer 29

A calorimeter

Question 30

What does a calorimeter experiment look like

Answer 30

DRAW IT

Question 31

How can you use a calorimeter to work out the enthalpy change of combustion

Answer 31

Record the volume of water Record the mass of the fuel before and after heating Record the temperature change in water Use q = m x c x ^t Find the moles of fuel burnt

Question 32

Why will the calculated change be less than the actual value

Answer 32

. Non standard conditions . Droughts affect the flame . Heat transferred to beaker. Surroundings instead of H2O/ Heat loss . Soot formed on beaker - incomplete combustion . Evaporation of fuel - weigh as soon as possible after extinguishing flame

Question 33

What are average bond enthalpies used for

Answer 33

For bonds that occur in different molecules

Question 34

What does the bond enthalpy depend on

Answer 34

The value depends on the bond environment

Question 35

What are the limitations of average bond enthalpy

Answer 35

Using average bond enthalpies rather than the actual energy involved The energy of individual bonds would be slightly different due to the different environments

Question 36

What is Hess’ law

Answer 36

The enthalpy change of a reaction is independent of the route taken if initial and final conditions are the same.

Question 37

What is the definition of average bond enthalpy

Answer 37

The average energy required to break one mole of a specified type of bond in gaseous molecules, averaged over a range of compounds

Question 38

Enthalpy change of a reaction definition

Answer 38

Enthalpy change that accompanies a reaction in the molar quantities stated in the equation under standard conditions with all reactants and products in standard state.