Entropy and Gibbs free energy

What does Gibbs Free Energy tell us?

• How much energy is given off by a reaction.

• The tendency of a reaction to become "random"

• How spontaneous a reaction is.

What information do we need to perform a calculation of Gibbs Free Energy?

• Enthalpy of the reaction.

• Entropy of the reaction.

• The temperature of the reaction in Kelvin.

• All of the above are needed.

Which of the following would most likely lead to a spontaneous reaction.

• A high negative enthalpy.

• A low negative enthalpy.

• A high positive enthalpy.

• A low positive enthalpy.

Tags

NGSS.HS-PS1-4

What are the best conditions to lead towards a spontaneous reaction?

• high negative enthalpy, high temp, high negative entropy

• high positive enthalpy, high temp, high negative entropy

• high negative enthalpy, low temp, high positive entropy

• high negative enthalpy, high temp, high positive entropy.

Entropy increases from solid, liquid to gas. Why?

• Molecular disorder increases
• Molecular randomness decreases
• Molecules are more energetic
• Molecules are more reactive

Tags

NGSS.HS-PS3-4

Which represents a decrease in entropy?

• sublimation of CO₂

• boiling water

• condensation of steam on cold glass

• NaCl dissolving in water

Which sample has the lowest entropy?

HINT - Look at the phase of each chemical....

• 1 mole of KNO₃(l)

• 1 mole of KNO₃(s)

• 1 mole of H₂O(l)

• 1 mole of H₂O(g)

Which phase change represents a decrease in entropy?

• solid to liquid

• gas to liquid

• liquid to gas

• solid to gas

6. The formation ½ A₂ + 2 B₂ + C --> CAB₄ has an enthalpy of formation of -104 kJ and a change in entropy of -60.8 J/K at 30 °C. What is the free energy and spontaneity of the reaction?

• -85.6 kJ, spontaneous

• -18.3 kJ, not spontaneous

• +18.3 kJ, spontaneous

• +85.6 kJ, not spontaneous

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Predict the signs of ΔH , ΔS and ΔG for the reaction:

Mg(s) --> Mg(g)

• Δ H = - , Δ S = + and Δ G = - (all temperature)

• Δ H = + , Δ S = + and Δ G = - (At all temperature)

• Δ H = + , Δ S = + and Δ G = - (At low temperature)

• Δ H = + , Δ S = + and Δ G = - (At high temperature)

Tags

NGSS.HS-PS1-4