Enthalpy

Question 1

2 facts about Endothermic reactions

Answer 1

-Energy of products is greater than energy of reactants
-Energy moves from the surrounding to the system (surroundings get colder)

Endothermic reactions are BOND BREAKING processes that include melting and boiling

Question 2

2 facts about exothermic reactions

Answer 2

-Energy of products is less than energy of reactants
-Energy is lost from the system to the surroundings

Exothermic reactions are BOND FORMING PROCESSES like combustion, condensation and freezing

Question 3

What is enthalpy?

Answer 3

The heat content of reactants or products in a reaction (H)

Question 4

What is the change in enthalpy?

Answer 4

Change in enthalpy (🔼H) is the change in heat content as reactants are transformed into products

Question 5

If (🔼H) is positive:

Answer 5

Heat energy is increased so reaction is endothermic

Question 6

If (🔼H) is negative:

Answer 6

Reaction is exothermic

Question 7

Name the 6 types of enthalpy:

Answer 7

🔺rH
🔺fusH
🔺vapH
🔺subH
🔺cH^0
🔺fH^0

Question 8

🔺rH means

Answer 8

Enthalpy of a reaction

Question 9

🔺fusH means

Answer 9

Molar heat of fusion (melting)
Heat change as one mole of substance goes from solid to liquid
ENDOTHERMIC

Question 10

🔺vapH means

Answer 10

Molar heat of vaporisation (boiling)
Heat change as one mole of substance goes from liquid to gas
ENDOTHERMIC

Question 11

🔺subH means

Answer 11

Molar heat of sublimation
Heat change as one mole of substance goes from solid to gas
Endothermic

Question 12

🔺cH^0 means

Answer 12

Standard enthalpy of combustion
ALWAYS EXOTHERMIC REACTION
Enthalpy change when one mole of substance is completely burnt in oxygen with all reactants and products in their standard states
Reaction occurs at 25^0

Question 13

🔺fH^0 means

Answer 13

Standard enthalpy of formation
Enthalpy change when one mole of substance is formed from its elements with all reactants and products in their standard states
Occurs at 25^0 and one atmosphere pressure
🔺fH for a pure element is 0

Question 14

🔺rH=

Answer 14

{🔺fHproducts -{fH reactants

Question 15

Hess’s Law

Answer 15

The enthalpy change for a reaction is independent of the way in which a reaction proceeds and depends only on the initial conditions of the reactants and the final conditions of the products.

Question 16

Must carry out reaction in a…

Answer 16

Closed system

Question 17

Specific heat capacity

Answer 17

The amount of energy required to raise the temperature of 1g of that substance by one degree.

Question 18

Define the letters in q=mc🔺T

Answer 18

q= energy change
m=mass of water
c= specific heat capacity
🔺T= temperature change (final-initial)

Question 19

🔺H=

Answer 19

-q/n

Question 20

n=

Answer 20

m/M

Question 21

c=

Answer 21

n/v

Question 22

What is entropy?

Answer 22

A measure of randomness or disorder in a chemical system

Question 23

Creating disorder…? Creating order…?

Answer 23

Releases energy
Requires energy

Question 24

more particles means

Answer 24

More entropy

Question 25

Less particles..?

Answer 25

Less energy

Question 26

Solids have more or less entropy than gas?

Answer 26

Less

Question 27

Entropy change

Answer 27

🔺S

Question 28

If reaction is exothermic, the entropy of surroundings…?

Answer 28

Increases

Question 29

If the reaction is endothermic, the entropy of surroundings…?

Answer 29

Decreases

Question 30

Spontaneity: If the entropy of a system and its surroundings are increasing, the reaction must…?

Answer 30

Be Spontaneous

Question 31

Spontaneity: If the entropy of a system and its surroundings are decreasing, the reaction must…?

Answer 31

Not be spontaneous