# Chemical Reaction General Chemistry – Exam

### Chemical Reaction General Chemistry – Exam

This exam is about Chemical Reaction General Chemistry – Exam.

The first and second laws of thermodynamics are written below. Complete the sentences by filling in the blanks.

First Law: The energy of the _________ is constant.

Second Law: For any spontaneous process the entropy of the _______ increases.

Universe, Universe

Consider a process in which 220 kJ of work are performed on a gaseous system at 37oC. If at the end of the process the temperature of the system is still 37oC, what can you say about heat involved in this process?

q = -220 kJ

At room temperature the reaction of iron(III) oxide with carbon to produce solid metallic iron and carbon monoxide has K = 10-58 and a positive ΔSo.

2Fe2O3 (s) + 3C (s) → 4Fe (s) + 3CO2 (g)

Despite its very low K value at room temperature this reaction is widely used in industry to convert iron oxide into iron metal at very high temperatures. In fact, more than 100000000 tons of iron is made this way annually. Based on this information, what can we infer about this reaction at very high temperatures?

The value of Δ Ho for the process must be positive and K increases with temperature.

IF K > 1 for a reaction at 298K what can be said about the reaction at this temperature?

ΔGo < 0

Use the information below to find Δfor the synthesis of ammonia from hydrazine and hydrogen:

N2H4(l) + H2(g) → 2NH3(g)

N2H4(l) + CH4O(l) → CH2O(g) + N2(g) + 3H2(g)    ΔH = -37 kJ

0.5N2(g) + 1.5H2(g) → NH3(g)                                ΔH = -23 kJ

CH4O(l) → CH2O(g) + H2(g)                                    ΔH = -65 kJ

18 kJ

The standard heat of combustion of ethanol, C2H5OH, is 1372 kJ per 1 mole of ethanol. How much heat (in kJ) would be liberated by completely burning a 20.0 g sample of ethanol? (MM(C2H5OH)=46 g/mol)

597 kJ

Imagine you have a 120 g sample of solid tin at 25oC. You add the metal to a crucible and heat it until you have melted all of the tin. If you want to calculate how much heat you needed for this process, which of the following equations would you use?

Some constants you may need:

Sn(s) c = 0.21 J/g-oC

Sn(l) c = 0.050 J/g-oC

c(Sn,fussion) = 59.2 J/g

c(Sn,evaporation) = 2.49 kJ/g MP(Sn) = 232oC

q = 0.21*120*(232-25) + 59.2*120

What is the change in internal energy of a sample of gas if it does 9 kJ of work and at the same time 15 kJ of heat is transferred to the sample?

+6 kJ

What can you say about the entropy change in the following reaction?

ΔS > 0, ΔSSURR < 0, ΔSUNIVERSE is unknown

Consider the following reaction:

2NO2(g) ⇌ 2NO(g) + O2(g)

Which of the following statements would indicate that this reaction is NOT spontaneous at room temperature?

H > 0  and | ∆S | < |∆Ssurr |

If for a certain reaction mixture ΔGo>0 and ΔG <0, which of the following statements about this reaction mixture is true?

From this mixture the reaction will proceed forward to reach equilibrium and K <1 for the reaction.

Which one of the following reactions do you expect to exhibit a decrease in entropy?

CH2O (g) + O(g) → H2O (l) + CO(g)

Consider the table of thermodynamic data table below to find the value of ∆Go for the formation of ammonia gas (1 mol) at 375K?

-8.7 kJ/mol

Which of the following must be true for a spontaneous endothermic process?

ΔS > 0 and | ΔS | > | ΔSSURR |

What is the free energy, per mole, to transport sodium ions up a concentration gradient from 0.020M to 0.080M at 37oC?

3.6 kJ

Which of the following correctly expresses the relationship between the enthalpy of a system and the entropy of the surroundings?

SSURR˚ = -∆H˚/T

The normal boiling point of a substance is defined to be the temperature at which the liquid phase of the substance is in equilibrium with the gas phase at 1 atm pressure. The normal boiling point of methanol is 80oC and H vap = 38 kJ/mol. What is the Svap value?

110 J/mol-K

At 8oC the pH of pure water is 7.31. What is ΔGo for water dissociation at this temperature?

78.6 kJ/mol

If a chemical reaction results in a gas expansion we say that work is done________ and the sign of the work is __________.

by the system, w < 0

Consider the decomposition of hydrogen fluoride:

2HF(g) → H2(g) + F2(g)

Given that at 298KΔGo = 38.3 kJ, [HF] = 0.070 atm, [H2] = 0.025 atm and [F2] = 0.0035atm, which of the following statements about this reaction at 298K is correct?

Under these conditions Q > K and the reaction will be spontaneous in the reverse direction.

Is the following reaction enthalpically or entropically driven?

2SO3(g) → 2SO2(g) + O2(g)    ΔH = 198.2 kJ

Entropically driven because it is endothermic and ΔSis positive.

If I add 100 kJ of heat to a 50.0 g sample of each of the following metals, which one will heat up the most slowly?

Mg

Given that at 298K for the reaction A3 + 6B → 3AB2 ΔHo = 75 kJ/mol, what is the ΔHo value for the reaction AB2 → (1/3)A3 + 2B?

-25 kJ/mol

Without doing any calculations, predict the signs of ∆Ho, ∆S˚, ∆HSURRo, ∆SSURR˚ and ∆Go for the reaction:

A(g) + B(g) → AB(g)

Ho < 0, ∆So < 0, ∆HSURRo > 0, ∆SSURRo  > 0 and ∆Go is unknown

Consider the following reaction:

2H2(g) + O2(g) → 2H2O(g)      ΔHo = -484 kJ/mol

If you react 0.80 mol of H2(g) and 0.60 mol of O2(g), what is the heat for the reaction?

-194 kJ

Consider the following reaction:

C2H4(g) + H2O(g) ⇌ C2H5OH(g)       ΔHo = -45.8 kJ/mol

At 298K the equilibrium constant, KP, for this reaction is 28.5. What is ΔG for this reaction at 298K under the following conditions: p(C2H4) = p(H2O) = p(C2H5OH) = 3.0 atm?

-11.0 kJ/mol

Consider the following reaction:

CH4(g) + 2O2(g) → 2H2O(g) + CO2(g)        ΔH= -802.34 kJ

Given that ΔHo(CO2) =-393.51 kJ and ΔHo(CH4)=-74.81 kJ, what is the ΔHfor H2O?

-241.82 kJ

In an experiment 359 J of heat were spent to raise the temperature of a 57.0 g sample of an unknown alloy by 54.0oC. What is the heat capacity of this alloy?

0.117 J/g- oC

Consider the Haber process for the production of ammonia:

N2(g) + 3H(g) →2NH3(g)

This reaction is thermodynamically spontaneous at 298K, but becomes nonspontaneous at higher temperatures. Which of the following statements is true about this reaction under standard conditions at 298K?

Go, ∆Ho, and ∆So are all negative.

For any substance, the entropy change for vaporization is significantly higher than the entropy change for melting because _____________________.

particles in a gas state occupy much larger volume compared to a solid or liquid state

Consider the free energy diagram for the reaction R → P shown below. The reaction is _______, the equilibrium position is indicated by letter __________ and at point I__________.

spontaneous, III, ΔG < 0

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