Enthalpy Change

Question 1

What can cause enthalpy change to vary?

Answer 1

Conditions used

Enthalpy change can vary slightly depending on the conditions under which measurements are made.

Question 2

What is the standard condition used for?

Answer 2

Physical measurements such as enthalpy change

Standard condition is important for consistency in measurements.

Question 3

How is a standard physical value indicated in data tables?

Answer 3

Using a special standard sign ‘⦵’

This sign denotes values measured under standard conditions.

Question 4

What does a standard enthalpy change ΔH° refer to?

Answer 4

An enthalpy H change Δ under standard conditions ⦵

Units are usually KJ mol-1.

Question 5

What is the standard pressure in kPa?

Answer 5

100 KPa

This is close to one atmosphere, which is 101 KPa.

Question 6

What is the standard temperature usually stated in Kelvin?

Answer 6

298 K

This is equivalent to 25℃.

Question 7

What is the standard concentration for solutions?

Answer 7

1 mol dm-³

This applies specifically for solutions.

Question 8

What defines the standard state of a substance?

Answer 8

The physical state under standard conditions

Most data tables show standard state at 100 kPa and 298 K.

Question 9

What is the standard enthalpy change of a reaction ΔRH°?

Answer 9

Enthalpy change accompanying a reaction in molar quantities shown under standard conditions

This refers to the specific amounts in the balanced equation.

Question 10

What does the standard enthalpy change of formation ΔFH⦵ represent?

Answer 10

Enthalpy change when one mole of a compound is formed from its elements under standard conditions

This is a key concept in thermodynamics.

Question 11

For an element, what does ΔFH° refer to?

Answer 11

Formation of one mole of an element from its element

This reflects a unique case for elemental substances.

Question 12

What is the standard enthalpy change of combustion ΔCH°?

Answer 12

Enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions

This is crucial for understanding energy release in reactions.

Question 13

What does the standard enthalpy change of neutralisation ΔneutH°?

Answer 13

Energy change during a neutralisation reaction where 1 mole of H₂O is formed under standard conditions

This highlights the energy dynamics in acid-base reactions.