18.4 Quiz

Predict the direction of entropy change: CaCO3 (s) ➡️ CaO (s) + CO2 (g)

+ (less ordered), increasing

Predict the direction of entropy change: NH3 (g) + HCl(g)➡️ NH4Cl (s)

- (more ordered), decreasing

Which system has the lower entropy: 10g of sodium chloride crystals or a solution containing 10g of sodium chloride?

10g of sodium chloride crystals. Crystals more ordered and structured.

Which system has the lower entropy: 50 ml of liquid water or 50 ml of ice?

50 ml of ice. More ordered, structured, motionless, therefore lower entropy.

Explain why, under certain circumstances, a nonspontaneous reaction becomes spontaneous?

A change in state of reactant, due to change in temperature or pressure, may change the balance between delta S and delta H. Usually increasing overall temperature.

How does the free energy of a reaction help predict whether the reaction will be spontaneous?

A spontaneous reaction has a negative free energy

What part does entropy play in determining whether a chemical reaction is spontaneous or nonspontaneous?

An increase in entropy favors the spontaneous chemical reaction; a decrease favors the nonspontaneous reaction.

Is it true that all spontaneous processes are exothermic? Explain your answer.

No because it is Gibbs Free Energy that determines spontaneity not enthalpy.

What are 2 characteristics of spontaneous reactions?

Spontaneous reactions produce substantial amounts of products at equilibrium and release free energy

At normal atmospheric pressure, steam condenses to liquid water even though this is an unfavorable entropy change. Explain.

The favorable exothermic change of the condensation process offsets the unfavorable entropy change.

What is the sign (+ or -) of the Gibbs free-energy change in a spontaneous process?

The numerical value of delta G is negative in spontaneous processes because the system loses free energy.

What two factors determine the spontaneity of a reaction?

The size and direction of enthalpy changes and entropy changes together determine whether a reaction is spontaneous; that is, whether it favors products and releases free energy.

Supposed the products in a spontaneous process are more ordered than the reactants. Is the entropy change favorable or unfavorable?

Unfavorable •unfavorable entropy change is when the entropy decreases which it does when there is more order. If products are more ordered than reactants, the entropy has decreased making it unfavorable.

The products in a spontaneous process are more ordered than the reactants. Is this entropy change favorable or unfavorable?

Unfavorable. More ordered=less entropy.

What two factors together determine whether a reaction is spontaneous?

You need to know both the enthalpy change and entropy change to determine whether a chemical reaction is spontaneous.

Where does released free energy typically end up? Does free energy lost as heat ever serve a useful function? Explain.

•Released free energy typically ends up amongst the atmosphere. •It can be useful. Waste heat from chemical reactions in the body maintains body temp at 37 degrees C. Waste heat from industrial processes and electrical generation can be used to heat water and buildings.