Question 8.13: Predicting the Signs of ΔH, ΔS, and ΔG for a Reaction What a......

General Chemistry: Atoms First [1015060]

Predicting the Signs of ΔH, ΔS, and ΔG for a Reaction

What are the signs of ΔH, ΔS, and ΔG for the following nonspontaneous transformation?

STRATEGY

First, decide what kind of process is represented in the drawing. Then decide whether the process increases or decreases the entropy (molecular randomness) of the system and whether it is exothermic or endothermic.

worked example 8.13

Step-by-Step

The 'Blue Check Mark' means that this solution was answered by an expert.
Learn more on how do we answer questions.

The drawing shows ordered particles in a solid subliming to give a gas. Formation of a gas from a solid increases molecular randomness, so ΔS is positive. Furthermore, because we’re told that the process is nonspontaneous, ΔG is also positive. Because the process is favored by ΔS (positive) yet still nonspontaneous, ΔH must be unfavorable (positive). This makes sense, because conversion of a solid to a liquid or gas requires energy and is always endothermic.

Related Answered Questions

Question: 8.10

Using Bond Dissociation Energies to Calculate ΔH° Use the data in Table 8.3 to find an approximate ΔH° in kilojoules for the industrial synthesis of chloroform by reaction of methane with Cl2. CH4(g) + 3 Cl2(g) → CHCl3(g) + 3 HCl(g) STRATEGY Identify all the bonds in the reactants and products, ...

Verified Answer:

The reactants have four C-H bonds and three Cl-Cl ...

Question: 8.7

Using Hess’s Law to Calculate ΔH° Water gas is the name for the mixture of CO and H2 prepared by reaction of steam with carbon at 1000 °C: C(s) + H2O(g) → CO(g) + H2(g) “Water gas” The hydrogen is then purified and used as a starting material for preparing ammonia. Use the following information to ...

Verified Answer:

\begin{array}{ll}\mathrm{C}(\mathrm{s})+\ca...

Question: 8.12

Using the Free-Energy Equation to Calculate Equilibrium Temperature Lime (CaO) is produced by heating limestone (CaCO3) to drive off CO2 gas, a reaction used to make Portland cement. Is the reaction spontaneous under standard conditions at 25 °C? Calculate the temperature at which the reaction ...

Verified Answer:

At 25 °C (298 K), we have

\Delta G=\Delta H...

Question: 8.11

Predicting the Sign of ΔS for a Reaction Predict whether ΔS° is likely to be positive or negative for each of the following reactions: (a) H2C=CH2(g) + Br2(g) → BrCH2CH2Br(l) (b) 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g) ...

Verified Answer:

(a) The amount of molecular randomness in the syst...

Question: 8.9

Using Standard Heats of Formation to Calculate ΔH° Oxyacetylene welding torches burn acetylene gas, C2H2(g). Use the information in Table 8.2 to calculate ΔH°in kilojoules for the combustion reaction of acetylene to yield CO2(g) and H2O(g). STRATEGY Write the balanced equation, look up the ...

Verified Answer:

The balanced equation is

2 \mathrm{C}_2 \ma...

Question: 8.8

Using Standard Heats of Formation to Calculate ΔHº Calculate ΔHº in kilojoules for the synthesis of lime (CaO) from limestone (CaCO3), the key step in the manufacture of cement. CaCO3(s) → CaO(s) + CO2(g) ΔHºf[CaCO3(s)] = -1207.6 kJ/mol ΔHºf[CaO(s)] = -634.9 kJ/mol ΔHºf[CO2(g)] = -393.5 kJ/mol ...

Verified Answer:

\begin{aligned}\Delta H^{\circ} & =\lef...

Question: 8.6

Using Hess’s Law to Calculate ΔH” Methane, the main constituent of natural gas, burns in oxygen to yield carbon dioxide and water: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) Use the following information to calculate ΔH° in kilojoules for the combustion of methane: CH4(g) + O2(g) → CH2O(g) + H2O(g) ...

Verified Answer:

\begin{matrix} \begin{aligned} \mathrm{CH}_...

Question: 8.5

Calculating the Amount of Heat Released in a Reaction How much heat in kilojoules is evolved when 5.00 g of aluminum reacts with a stoichiometric amount of Fe2O3? 2 Al(s) + Fe2O3(s) → 2 Fe(s) + Al2O3(s) ΔH° = -852 kJ ...

Verified Answer:

The molar mass of Al is 26.98 g/mol, so 5.00 g of ...

Question: 8.4

Calculating ΔE for a Reaction The reaction of nitrogen with hydrogen to make ammonia has ΔH° = -92.2 kJ. What is the value of ΔE in kilojoules if the reaction is carried out at a constant pressure of 40.0 atm and the volume change is -1.12 L? N2(g) + 3 H2(g) → 2 NH3(g) ΔH° = -92.2 kJ ...

Verified Answer:

\begin{aligned}& \Delta E=\Delta H-P \D...

Question: 8.3

Calculating ΔH in a Calorimetry Experiment Aqueous silver ion reacts with aqueous chloride ion to yield a white precipitate of solid silver chloride: Ag^+(aq) + Cl^-(aq) → AgCl(s) When 10.0 mL of 1.00 M AgNO3 solution is added to 10.0 mL of 1.00 M NaCl solution at 25.0 °C in a calorimeter, a white ...

Verified Answer:

\begin{aligned}& \text { Specific heat ...