Entropy, Enthalpy and Free Energy

Which represents a decrease in entropy?

• sublimation of CO₂

• boiling water

• condensation of steam on cold glass

• NaCl dissolving in water

The entropy will usually increase when

• a molecule is broken into two or more smaller molecules

• a reaction occurs that results in an increase in the number of moles of gas

• a solid changes to a liquid

• all of these

Tags

NGSS.HS-PS3-4

Which sample has the lowest entropy?

• 1 mole of KNO₃(l)

• 1 mole of KNO₃(s)

• 1 mole of H₂O(l)

• 1 mole of H₂O(g)

Which phase of matter has the greatest degrees of freedom of motion and therefore the highest entropy.

• solid

• liquid

• gas

Tags

NGSS.HS-PS3-4

Given the change of phase:

CO₂(g) —> CO₂(s)

As CO₂(g) changes to CO₂(s), the entropy of the system

• decreases

• increases

• remains the same

Which of these reactions shows a DECREASE in entropy?

• CaCO₃(s) → CaO(s) + CO₂(g)

• 3O₂(g) → 2O₃(g)

• 2NH₃(g) → 3H₂(g) + N₂(g)

• C₆H₆(l) → C₆H₆(g)

Which reaction has a +ΔS ?

• H₂O(g) + CO₂(g) → H₂CO₃(aq)

• H₂(g) + I₂(g) → 2Hl(g)

• C₂H₂O₂(g) → 2CO(g) + H₂(g)

What is a spontaneous process ?

• slow process

• fast process

• process that needs an external intervention to occur

• process that does not need external intervention to occur / keep happening

A reaction has a positive ΔH and a positive ΔS. Which of the following is true?

• It will be spontaneous at all temperatures.
• It will be nonspontaneous at all temperatures.
• It will be spontaneous at low temperatures.
• It will be spontaneous at high temperatures.

Your enthalpy is high and negative but your entropy is also negative. What type of temperature would you want to get a spontaneous reaction?

• low

• high