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 and heats the surroundings

Question 7

Define “endothermic”

Answer 7

A reaction that takes in energy and cools the surroundings

Question 8

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

Answer 8

Positive - products end up with more energy than reactants absorbing energy from surroundings

Question 9

Define “enthalpy change”

Answer 9

Amount of energy transferred to and from surroundings when a reaction occurs in an open container

Question 10

Why are standard conditions used when calculating enthalpy change?

Answer 10

They are set conditions which allows us to compare enthalpy changes

Question 11

What temperature is used in standard conditions?

Answer 11

298K

Question 12

What pressure is used in standard conditions?

Answer 12

1atm

Question 13

What concentration is used in standard conditions?

Answer 13

1mol dm-3

Question 14

How do you convert K to degrees C?

Answer 14

Minus 273 from the kelvin value

Question 15

What are the 4 types of enthalpy change for AS?

Answer 15

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

Question 16

Define “standard enthalpy change of a reaction”

Answer 16

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

Question 17

Define “standard enthalpy change of a formation”

Answer 17

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

Question 18

Define “standard enthalpy change of a combustion”

Answer 18

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

Question 19

Define “standard enthalpy change of a neutralisation”

Answer 19

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

Question 20

Define “standard states”

Answer 20

A substance’s most stable state under standard conditions

Question 21

Are all combustion reactions positive/negative and why?

Answer 21

Negative because they are all exothermic

Question 22

What is the formula for calculating enthalpy change?

Answer 22

q = m x c x change in T

Question 23

What is the specific heat capacity of water?

Answer 23

4.18 J g-1k-1

Question 24

How does a bomb calorimeter work?(2)
Challenge beyond AS

Answer 24

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