AP Chemistry Spontaneity, Entropy, and Free Energy

The thermodynamic quantity that expresses the degree of disorder in a system is _

• entropy

• internal energy

• heat flow

• enthalpy

• bond energy

Which one of the following is always positive when a spontaneous process occurs?

• ΔH univ

• ΔH surr

• ΔS surr

• ΔS univ

• ΔS sys

ΔS will be positive for the reaction

• 2H2 (g) + O2 (g) -> 2H2O (g)

• 2NO2 (g) -> N2O4 (g)

• BaF2 (s) ->Ba2+ (aq) + 2F- (aq)

• 2Hg (l) + O2 (g) ->2HgO (s)

Tags

NGSS.HS-PS1-4

Which one of the following processes produces a decrease in the entropy of the system?

• dissolution of solid KCl in water

• mixing of two gases into one container

• freezing water to form ice

• melting ice to form water

Of the following, the entropy of gaseous __________ is the largest at 25eC and 1 atm.

• C2H2

• H2

• C2H6

• CH4

• C2H

What can be said about a chemical system that has reached a minimum in free energy?

• The system has achieved equilibrium.

• The reaction is complete.

• The system entropy is zero.

• The reaction is very fast.

Tags

NGSS.HS-PS1-6

For the reaction C2H6 (g) ->C2H4 (g) + H2 (g) ΔH^ο is +137 kJ/mol and ΔDS^οis +120 J/K œ mol. This reaction is

• nonspontaneous at all temperatures

• unreliable

• spontaneous only at high temperature

• spontaneous at all temperatures

• spontaneous only at low temperature

Tags

NGSS.HS-PS1-4

A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if ΔH is __________ and ΔS is __________.

• +, +

• -, -

• +, -

• -, +

• +, 0

For a reaction to be spontaneous under standard conditions at all temperatures, the signs of ΔH^Ο and ΔS^Ο must be __________ and __________, respectively.

• +, +

• +, -

• -, +

• -, -

• +, 0

In the Haber process, ammonia is synthesized from nitrogen and hydrogen: N2 (g) + 3H2 (g) ->2NH3 (g)

∆G at 298 K for this reaction is -33.3 kJ/mol.

The value of ∆G at 298 K for a reaction mixture that consists of 1.9 atm N2, 1.6 atm H2, and 0.65 atm NH3 is

• 3.86 x10³

• -1.8

• -40.5

• -7.25 x10³

• -104.5

Tags

NGSS.HS-PS1-5

NGSS.HS-PS3-1