Thermochemistry

Question 1

What is it meant by the “system” and the “surroundings”

Answer 1

The system consists of the molecules which are reacting and the surroundings is everything else.

Question 2

What is the energy transfer that occurs in both an endothermic and exothermic reaction?

Answer 2

Heat transfer

Question 3

What is it meant by the term “Standard states”

Answer 3

Standard states are the conditions in which the substance exists during standard conditions.

Question 4

What is it meant by the term “Standard conditions”

Answer 4

Standard conditions is the condition a substance would naturally be.

Question 5

What is the definition of Enthalpy of formation?

Answer 5

Enthalpy of formation is the energy required to produce 1 mole of product from its constituent atoms in their standard state at standard conditions.

Question 6

What is the definition of Enthalpy of combustion?

Answer 6

The Enthalpy of combustion is the energy requires to react 1 mole of product with oxygen under standard conditions.

Question 7

What is the definition of Enthalpy of vaporisation?

Answer 7

The Enthalpy of vaporisation is the amount of energy required to convert 1 mole of liquid to 1 mole of gas at its boiling point.

Question 8

What is the definition of Enthalpy of fusion?

Answer 8

The Enthalpy of fusion is the energy required to convert 1 mole of solid to 1 mole of liquid state at its melting point.

Question 9

What is the definition of Enthalpy of sublimation?

Answer 9

Enthalpy of sublimation is the amount of energy required to convert 1 mole of a solid to 1 mole of a gas in its gaseous state at the sublimation point.

Question 10

How to calculate the number of moles (n) from the mass (m) and molar mass (M)?

Answer 10

Use the formula (n=m/M)

Question 11

How to calculate the Enthalpy (^H) from the number of moles (n) and the Enthalpy change of reaction (^rH)

Answer 11

1. Calculate number of moles from formula (n=m/M)

2. Times the number of moles by the enthalpy change of reaction.

Question 12

How to calculate the amount of heat transferred?

Answer 12

Using the formula q=m x c x ^T

q=Amount of heat transfered

Question 13

What is the definition of specific heat capacity?

Answer 13

The amount of heat required to increase the temperature of one gram of water by 1c

Question 14

What does a high or low specific heat capacity tell us about different compounds?

Answer 14

Compounds with higher specific heat capacity’s are harder to heat, compounds with lower specific heat capacity’s are easier to heat.

Question 15

What does the term “Entropy” mean?

Answer 15

Entropy describes the disorder or randomness of a system

Question 16

Does Entropy increase or decrease as you go from a solid to a liquid to a gas?

Answer 16

It increases as there is more randomness.

Question 17

Why does Entropy increase when more moles of a substance are produced?

Answer 17

There is more disorder therefore an increased Entropy.

Question 18

What is a spontaneous reaction?

Answer 18

Spontaneous reactions occur by themselves without any external help such as an extra input of energy

Question 19

What is a non-spontaneous reaction?

Answer 19

Un-spontaneous reactions can only occur by external drive such as an input of energy.

Question 20

What are the features of reactions that are spontaneous?

Answer 20

Exothermic + Increase of Entropy

Question 21

What are the features of reactions that are un-spontaneous?

Answer 21

Endothermic + Decrease of Entropy

Question 22

Why can it be hard to decide on whether a reaction is spontaneous or not?

Answer 22

In the case where you have both features of spontaneous and non-spontaneous reactions.

Question 23

What is hess’s law?

Answer 23

The total Enthalpy change during a chemical reaction is the same whether the reaction endured one step or multiple component reactions.

Question 24

Define ^rH

Answer 24

The amount of energy or heat absorbed in a reaction.

Question 25

Define ^cH

Answer 25

The change in energy when one mole of a reactant is reacted with oxygen in a combustion reaction under standard conditions.

Question 26

Define ^fH

Answer 26

The change in enthalpy when one mole of a substance, under standard conditions, is formed from pure elements.

Question 27

Define ^fusH

Answer 27

The amount of energy required to change 1 mole of a substance from a solid to a liquid at the substances melting point.

Question 28

Define ^vapH

Answer 28

The amount of energy required to change 1 mole of a substance from a liquid to a gas at the substances boiling point.

Question 29

Define ^subH

Answer 29

The amount of energy required to change 1 mole of a substance from a solid to a gas at the substances sublimation point.

Question 30

What is the calorimeter?

Answer 30

The piece of equipment used to measure the heat energy absorbed or released during a reaction.

Question 31

What is Calorimetry?

Answer 31

The science associated with determining the changes in energy of a system by measuring the heat exchanged with its surroundings.

Question 32

What is “Gibbs free energy”?

Answer 32

The prediction of the spontaneity of a reaction. Takes into consideration both the enthalpy and entropy changes.

Question 33

What is the heating curve?

Answer 33

A graph of temperature versus time for a substance where energy is added at a constant rate.

Question 34

What is latent heat?

Answer 34

The heat energy that is released or absorbed in the changing of the state of a substance.

Question 35

What are the typical standard conditions?

Answer 35

25 degrees, 298.15 K, & 101 kPa