CHEMISTRY- ENERGY CHANGES IN INDUSTRY

Question 1

What happens in exothermic reactions

Answer 1

Energy is released from reactants to surroundings
Temp of surroundings increases

Question 2

What is the symbol for enthalpy change

Answer 2

Delta H

Question 3

What happens in endothermic reactions

Answer 3

Energy takes from surroundings to reactions

Temp of surroundings decreases

Question 4

Name diatomic elements

Answer 4

O2
H2
I2
Br2
Cl2
F2
N2

Question 5

What is the standard enthalpy of combustion

Answer 5

Enthalpy change when 1 mole of a substance and it’s standard state burns completely in oxygen under standard conditions of 298k and one bar pressure.

Question 6

Give an example of standard enthalpy of formation

Answer 6

H2 + 1/2 O —> H2O

Question 7

What is the standard formation of water

Answer 7

L

Question 9

What is the standard enthalpy of formation in their standard states

Answer 9

Zero

Question 10

Why is the enthalpy of formation of Na zero

Answer 10

Na is an element in its standard state

Question 11

State why the enthalpy of formation of liquid Na is not zero

Answer 11

Liquid is not sodium’s standard state

Question 12

What is the standard enthalpy of formation

Answer 12

Enthalpy change when one mole of a substance is formed from its element under standard conditions of 298k and one bar pressure

Question 13

What do standard enthalpies of combustion have

Answer 13

Almost always have negative values

Question 14

Is burning a substance in oxygen exothermic or endothermic

Answer 14

Exothermic

Question 15

What happens to substance that cannot be combusted

Answer 15

They have zero enthalpy of combustion

Question 16

What types of substances cannot be combusted

Answer 16

Water
Carbon dioxide
And other oxides

Question 17

Why may the enthalpy of combustion of a compound be difficult to measure

Answer 17

Incomplete combustion may occur

Question 18

What do ions bond with

Answer 18

Water molecules

Question 19

What is the hydration of ions

Answer 19

The ions bond with water molecules
Positive ions will be attracted to the slightly negative oxygen in water molecules
Whilst negative ions will be attracted to the slightly positive hydrogens in water molecules

Question 20

What is Hess law

Answer 20

Reaction may have a very high activation energy
Reaction rate may be too slow
Possibility of competing reactions

Question 21

What is hess law used for

Answer 21

To calculate an enthalpy change indirectly

Question 22

name the type of reaction taking place when pentane burns in oxygen

Answer 22

combustion

Question 23

explain how exothermic processes affect their surroundings

Answer 23

releases heat from the system to the surroundings and the tempreture will increase

Question 24

state what is meant by the term standard enthalpy change of formation

Answer 24

when 1 mole of compound is formed from its elements under standard condition

Question 25

state what is meant by the term enthalpy change of combustion

Answer 25

when 1 mole of a substance is combusted completely in oxygen

Question 26

give one reason why the standard molar enthalpy change of formation of ethanol can not be measured directly

Answer 26

there are potentially other products and activation energy is too high

Question 28

What is the definition of an enthalpy change?

Answer 28

The measure of heat given out or taken in during a process

Question 29

Why is enthalpy change used instead of energy?

Answer 29

Because we cannot easily measure energy changes

Question 30

Why is enthalpy easy to use?

Answer 30

They are measured under constant pressure That atmosphere is at a constant pressure, so we require no extra equipment

Question 31

What type of enthalpy change does exothermic reaction have?

Answer 31

Negative

Question 32

What type of enthalpy change does endothermic reaction have?

Answer 32

Positive

Question 33

What is combustion?

Answer 33

An exothermic process that gives out heat

Question 34

What are the standard conditions for enthalpy change

Answer 34

Pressure of one bar Temperature of 298 Kelvin Substances in its most stable state under the above conditions

Question 35

What type of process is bond breaking?

Answer 35

Endothermic

Question 36

What type of process is bond making?

Answer 36

Exothermic

Question 37

What is the process used to extract aluminium from aluminium oxide?

Answer 37

Electrolysis

Question 38

Explain why the structure of aluminium oxide makes the compound resist to high temperature

Answer 38

Because it has a strong intermolecular forces Has high, melting point Contains strong electrostatic forces between the ions Has a giant ionic structure

Question 39

What is the temperature condition for Kelvin for standard conditions

Answer 39

298

Question 40

What is the standard condition for pressure?

Answer 40

100 Kpa

Question 41

Explain why the standard enthalpy change of formation for hydrogen gas is 0 kgMol-1

Answer 41

Hydrogen gas is an element on standard conditions so no change occurs

Question 42

Name an organic compound that can be dissolved in water to manufacture hydrogen by electrolysis

Answer 42

Sodium chloride

Question 43

State one use of short chain alkanes

Answer 43

Combustion

Question 44

Explain how vanadium oxide acts as a catalyst

Answer 44

The vanadium oxide is regenerated by the end of the reaction Vanadium oxide is oxidised by oxygen