Thermodynamics

A reaction has both positive ∆S° and ∆H° values. From this information alone, you can conclude that the reaction

• can be spontaneous at any temperature.

• cannot be spontaneous at any temperature.

• has a spontaneity that is temperature dependent, and it spontaneous at lower temperatures.

• has a spontaneity that is temperature dependent, and it spontaneous at higher temperatures.

Which of the following is not expected to have a value of zero at 25°C and 1 atm?

• ∆H°_f for F_{2 (g)}

• ∆G°_f for Li_(s)

• S° for Fe_(s)

• ∆H°_f for Mg_(s)

Tags

NGSS.HS-PS1-4

Consider this hypothetical reaction (at 375 K). The free energies in kJ/mol at this temperature are given below each substance in parentheses. What is the value of Gibbs free energy for the reaction at this temperature? Is the reaction spontaneous?

• -300.0 kJ; spontaneous

• 0.00 kJ; at equilibrium

• 300.0 kJ; non-spontaneous

• 600.0 kJ; non-spontaneous

Tags

NGSS.HS-PS1-4

A certain non-spontaneous reaction has ∆H of 12.3 kJ and a ∆S of 42 J/K. At approximately what temperature would the reaction become spontaneous?

• -20°C

• 0°C

• 20°C

• 100°C

A student volunteers to bring ice tea to a class picnic. She boils water to which she has added tea bags. Time is running short, so she places hot tea into an insulated, steel container, adds some ice cubes then seals the container. Assume that there is no heat exchange with the surroundings. Which of the following would be true?

• The total energy and entropy both remain the same.

• The total energy decreases while the entropy increases.

• The total energy and entropy decreases.

• None of the above.

Tags

NGSS.HS-PS3-4

Which of the following is true when ice melts?

• ∆H<0 ∆S<0

• ∆H=0 ∆S=0

• ∆H<0 ∆S>0

• ∆H>0 ∆S>0

Which of the following is true for the condensation of benzene, C₆H₆?

• ∆H°>0, ∆S°>0

• ∆H°>0, ∆S°<0

• ∆H°<0, ∆S°>0

• ∆H°<0, ∆S°<0

Tags

NGSS.HS-PS1-4

In which of the following four processes is there an increase in entropy?

• all of the above

• I and II only

• I and IV only

• III and IV only

Tags

NGSS.HS-PS3-4

For endothermic reactions at constant pressure

• ∆H>0

• ∆G<0

• ∆S>0

• ∆S<0

Tags

NGSS.HS-PS1-4

At a certain temperature C_(s) + O_{2 (g)} ⟶ CO_{2 (g)} has a ∆G of -339.4 kJ. This means that at this temperature

• the system is at equilibrium.

• gaseous carbon dioxide is unstable.

• gaseous carbon dioxide spontaneously forms.

• this system has a high reaction rate.