DF1: Thermochemistry

Question 1

Define “thermochemistry”

Answer 1

The study of energy and heat associated with chemical reactions

Question 2

Define “exothermic”

Answer 2

A reaction that gives out energy and heats surroundings

Question 3

During an exothermic reaction, are bonds formed/broken?

Answer 3

Formed

Question 4

During an exothermic reaction, is energy released/taken in?

Answer 4

Released

Question 5

Where does energy released from an exothermic reaction go?

Answer 5

Its lost to the reaction’s surroundings and heats them up

Question 6

Is enthalpy change positive/negative for exothermic reactions and why?

Answer 6

Negative - products end up with less energy than reactants

Question 7

Define “endothermic”

Answer 7

A reaction that takes in energy and cools the surroundings

Question 8

During an endothermic reaction, are bonds formed/broken?

Answer 8

Broken

Question 9

Is enthalpy change positive/negative for endothermic reactions and why?

Answer 9

Positive - products end up with more energy than reactants

Question 10

Define “enthalpy change”

Answer 10

Amount of energy transferred to and from surroundings

Question 11

Why are standard conditions used when calculating enthalpy change?

Answer 11

They are set conditions which allows us to compare enthalpy changes

Question 12

What temperature is used in standard conditions?

Answer 12

298K

Question 13

What pressure is used in standard conditions?

Answer 13

1atm

Question 14

What concentration is used in standard conditions?

Answer 14

1moldm-3

Question 15

How do you convert K to degrees C?

Answer 15

Minus 273

Question 16

What are the 4 types of enthalpy change?

Answer 16

• Standard enthalpy change of a reaction
• Standard enthalpy change of formation
• Standard enthalpy change of combustion
• Standard enthalpy change of neutralisation

Question 17

Define “standard enthalpy change of a reaction”

Answer 17

Enthalpy change when one mole of matter is transformed by a chemical reaction under standard conditions

Question 18

Define “standard enthalpy change of a formation”

Answer 18

Enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions

Question 19

Define “standard enthalpy change of a combustion”

Answer 19

Enthalpy change when 1 mole of a substance is completely burned in oxygen, under standard conditions

Question 20

Define “standard enthalpy change of a neutralisation”

Answer 20

Enthalpy change when acid reacts with alkali to form 1 mole of water under standard conditions

Question 21

Define “standard states”

Answer 21

A substance’s most stable state under standard conditions

Question 22

Are all combustion reactions positive/negative and why?

Answer 22

Negative because they are all exothermic

Question 23

What is the formula for calculating enthalpy change?

Answer 23

q=m x c x change in T

Question 24

What is the specific heat capacity of water?

Answer 24

4.18Jg-1k-1

Question 25

How does a bomb calorimeter work?(2)

Answer 25

• Fuel is ignited electrically and burns oxygen inside the pressurised vessel
• Energy is transferred to the surrounding water

Question 26

What is measured in a bomb calorimeter?

Answer 26

Temperature rise

Question 27

How is the experiment conducted in a bomb calorimeter?

Answer 27

At a constant volume in a closed container

Question 28

Why is the fuel in a bomb calorimeter burnt under pressure?

Answer 28

To increase the number of successful collisions leading to complete combustion of the sample

Question 29

Why is a bomb calorimeter more accurate than a simple calorimeter?

Answer 29

Low heat losses