2.1 Thermochemistry

Question 1

Exothermic reaction

Answer 1

Is a reaction that releases energy to the surroundings (creates a temperature increase) and the ΔH is negative

Question 2

Endothermic reaction

Answer 2

Is a reaction that takes in energy from the surroundings (creates a temperature drop) and the ΔH is positive

Question 3

Enthalpy

Answer 3

The heat content of a system at constant pressure

Question 4

Enthalpy change

Answer 4

The heat added to a system at constant pressure

Question 5

Chemical system is made up of the … and the …

Answer 5

Reactants
Products

Question 6

What are the units for Enthalpy

Answer 6

Joules (J) or Kilojoules (kJ)

Question 7

ΔH = … - …

Answer 7

H_products
H_reactants

Question 8

For exothermic reactions H_products … H_reactants

Answer 8

H_products < H_reactants

Question 9

For endothermic reactions H_products … H_reactants

Answer 9

H_products > H_reactants

Question 10

Principle of conservation of energy

Answer 10

Energy cannot be created or destroyed only changed from one form to another

Question 11

Standard conditions for temperature is …

Answer 11

298K or 25°C

Question 12

Standard conditions for pressure is …

Answer 12

1 atm or 101,000Pa

Question 13

What is the standard state of a substance

Answer 13

the substance in its pure form at 1atm and the stated temperature (normally 298K)

Question 14

What is the symbol for standard enthalpy change

Answer 14

ΔH^θ

Question 15

What is the symbol for standard enthalpy change of formation

Answer 15

Δ_fH^θ

Question 16

Enthalpy change of formation

Answer 16

Is the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions.

Question 17

The “per mole” refers to the formation of one mole of … or the product

Answer 17

compound

Question 18

What are the units for Δ_fH^θ

Answer 18

kJmol^-1

Question 19

What is the symbol for standard enthalpy change of combustion

Answer 19

Δ_cH^θ

Question 20

Enthalpy change of combustion

Answer 20

Is the enthalpy change when one mole of a substance is completely combusted in oxygen under standard conditions.

Question 21

The “per mole” refers to the … being combusted not the quantity of products formed

Answer 21

substance

Question 22

What is the symbol of Enthalpy change of reaction

Answer 22

Δ_rH

Question 23

Enthalpy change of reaction

Answer 23

Is the enthalpy change in a reaction between the number of moles of reactants shown in the equation for the reaction.

Question 24

Δ_rH^θ = …(products) - ΣΔ_fH(reactants)

Answer 24

ΣΔ_fH

Question 25

Hess's law

Answer 25

The total enthalpy change for a reaction is independent of the route taken from the reactants to the products.

Question 26

ΔH₁ = ΔH_... + ΔH_...

Answer 26

1. 2 2. 3

Question 27

When using enthalpy changes of combustion use: Δ^cH = ΣΔ_cH(...) - ΣΔ_cH(...)

Answer 27

1. reactants 2.products

Question 28

When using enthalpy changes of formation use: Δ^fH = ΣΔ_fH(...) - ΣΔ_fH(...)

Answer 28

1. products 2. reactants

Question 29

Bond enthalpy

Answer 29

Is the enthalpy required to break a covalent X - Y bond into atoms X and Y, all in the gas phase

Question 30

Average bond enthalpy

Answer 30

Is the average value of the enthalpy required to break a given type of covalent bond in the molecules of a gaseous species

Question 31

q = mcΔT

Answer 31

q = the amount of heat transferred m = the mass of the solution c = the specific heat capacity of the solution ΔT = the temperature change

Question 32

What is the specific heat capacity of water?

Answer 32

4.18Jg^-1K^-1