3.1.2

Question 1

What is enthalpy?

Answer 1

the heat energy stored in a chemical system

Question 2

How do we measure enthlpy?

Answer 2

MEASURE energy released to the surroundings or absorbed

Question 3

What is the standard pressure?

Answer 3

100kPa

Question 4

What is the standard temp?

Answer 4

298K or 25 degrees

Question 5

What is the standard concentration?

Answer 5

1 Mol dm-3

Question 6

What is the standard state of C?

Answer 6

solid

Question 7

What is the standard enthalpy change of combustion?

Answer 7

enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions

Question 8

What is the standard enthalpy change of formation?

Answer 8

enthalpy change when 1 mole of a substance is formed from it’s elements under standard conditions

Question 9

Why are experimental values for the standard enthalpy of combustion lower than data book values?

Answer 9

heat is lost despite insulation - not all energy transferred to water

chance of incomplete combustion

non standard conditions

Question 10

What is enthalpy change of neutralisation?

Answer 10

enthalpy change when an aqueous acid neutralises an aqueous base to form 1 mole of water

Question 11

What is Hess’s law?

Answer 11

more than 1 route possible
initial and final substances are the same
overall enthalpy change is the same

Question 12

What is bond enthalpy?

Answer 12

when 1 mole of a covalent bond is broken in gaseous conditions

Question 13

Why can bon breaking be exothermic sometimes?

Answer 13

more energy released by bond breaking than bond making