chem preview assignments march 27, 29, 31

Match the value of the Gibbs free energy change for a reaction with its implication.

G < 0 --> spontaneous G > 0 --> nonspontaneous G = 0 --> process at equilibrium

Oxidation involves the _____ of electrons, while reduction involves the _____ of electrons.

loss; gain

For a chemical reaction, ∆S°rxn = ΣnS°(_________) − ΣnS°(_________).

product(s) ; reactant(s)

Match each element with its most common oxidation number (assuming it is in a polar covalent or ionic bond).

Na --> +1 F --> -1 O --> -2 (or -1) Ca --> +2

Match the oxidation number of chlorine with the appropriate chemical compound.

NaClO4 --> +7 HCl --> -1 KClO --> +1 RbClO3 --> +5

Given the balanced chemical equation CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g), which of the following equations should be used to calculate the total entropy change for this reaction? (States of matter have been omitted for simplification.)

S[CO2] + 2(S[H2O]) - S[CH4] - 2(S[O2])

Under what conditions will the reaction of graphite shown below be spontaneous? C (s) + 2Cl2 (g) → CCl4 (g); ΔH° = -106.7 kJ

Spontaneous only at low T

Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T (at constant pressure so qsys = ΔHsys)? Select all that apply.

ΔSsurr is inversely proportional to temperature. If ΔHsys is negative, ΔSsurr will be positive.

When heat is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. Which of the following reflect this relationship (at constant pressure)?

ΔSsurr = - qsys/T ΔSsurr = - ΔHsys/T

Match the relative values of Q and K with the associated value of ΔG.

Q < K --> G < 0 Q > K --> G > 0 Q = K --> G = 0

Consider the chemical reaction 2SO3 (g) → O2 (g) + 2SO2 (g), for which ΔH° = +198.4 kJ and ΔS° = +187.9 J/K. Which of the following statements correctly describe the effect of temperature on the spontaneity of this reaction? Select all that apply.

The reaction is spontaneous only at higher temperatures. The reaction will become more spontaneous as the temperature increases.

Which of the following reactions result in the oxidation of sulfur? Select all that apply.

S8 + 8O2 → 8SO2 SO2 + H2O2 → H2SO4

A reaction that results in an overall increase in the number of gas molecules has a positive sign for ΔSrxn. Select the statement that correctly explains why.

The entropy of a substance in a gas phase is much higher than its entropy in the liquid or solid phase.

A reaction that produces more moles of gas will increase the entropy of the system because molecules in the gas phase have _____ than those in the condensed phases.

greater dispersal of energy

If a given process proceeds spontaneously toward the products, the value of the reaction quotient Q is _____ the equilibrium constant K and ΔG for the reaction will be _____.

less than; negative

If the oxidation number of a substance increases (becomes more positive), that substance has been ________ ; if the oxidation number decreases (becomes more negative), that substance has been __________.

oxidized; reduced

If a substance causes another substance to be oxidized, that substance is a(n) __________ agent. Likewise, the substance that is oxidized in an electrochemical reaction is always the ___________ agent.

oxidizing; reducing

When ΔG (the change in free energy) for a reaction is less than zero (negative), the reaction is _____ and the entropy change (ΔS) for the universe is _____.

spontaneous; positive