13049 Chemistry Practice Problems

1.560 x 10-4 mol of an unidentified gaseous substance effuses through a tiny hole in 98.8 s.

Under identical conditions, 1.749 x 10-4 mol of argon gas takes 84.9 s to effuse. 

What is the molar mass of the unidentified substance (in g/mol)? 

The percentage C by mass in the above unidentified substance is 53.0%. It may also contain H and/or O, but no other element. 

What is the molecular formula of the substance? 

In typing this formula use the convention of C first, H second and O last. For example, C6H8O2 would be C6H802.) 

Under identical conditions, how many moles of acetylene (C2H2) gas would effuse in 86.5 s? 

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Enter your answer in the provided box. 

The vapor pressure of ethanol is 100 mmHg at 34.9°C. What is its vapor pressure at 64.5°C? 

(ΔHvap for ethanol is 39.3 kJ/mol.) 

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A sample of an ideal gas has a volume of 3.15 L at 10.20°C and 1.50 atm. What is the volume of the gas at 20.80°C and 0.987 atm?  

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For the reaction

H2 (g) + C2H(g) → C2H6 (g)  

ΔG° = -100.7 kJ and ΔS° = -120.7 J/K at 301 K and 1 atm. 

This reaction is (reactant, product) ____________ favored under standard conditions at 301 K.

The standard enthalpy change for the reaction of 2.40 moles of H2(e) at this temperature would be ___________ kJ.

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For the reaction 

Fe3O4 (s) + 4H2 (g) → 3Fe (s) + 4H2O (g) 

ΔH° = 151.2 kJ and ΔS° = 169.4 J/K 

The standard free energy change for the reaction of 2.33 moles of Fe3O4(g) at 311 K, 1 atm would be ___________.

This reaction is (reactant, product) ____________ favored under standard conditions at 311 K.

Assume that ΔH° and ΔS° are independent of temperature. 

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A chemist measures the energy change ΔH during the following reaction: 

CH4 (g)+2O2 (g) → CO2 (g) + 2H2O (l)     ΔH = -882 kJ.

Use the information to answer the following questions. 

The reaction is:

                   (i) endothermic. 

                   (ii) exothermic. 

Suppose 84.2 g of CH4 react. Will any heat be released or absorbed?

                   (i) Yes, absorbed. 

                   (ii) Yes, released. 

                   (iii) No. 

If you said heat will be released or absorbed in the second part of this question, calculate how much heat will be released or absorbed. 

Round your answer to 3 significant digits.

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For the reaction 

2Fe (s) + 3Cl (g) → 2FeCl3 (s) 

ΔG° = -688.5 kJ and ΔS° = -440.3 J/K at 251 K and i atm. 

This reaction is (reactant, product) ____________ favored under standard conditions at 251 K.

The standard enthalpychanige for the reaction of 2.07 moles of Fe (s) at this temperature would be __________ kJ.

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392 K = ? °F

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-160°C = ? °F

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Write the equilibrium-constant expression for the reaction 

A (s) + 3B (l) ⇌ 2C (aq) + D (aq)

in terms of [A], [B], [C), and [D] as needed. 

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The reaction for producing glucose in plants, called photosynthesis, is 

6CO2 + H2O light→ C6H12O6 + 6O2

If a plant produces 9.36 mol of  C6H12O6, how many moles of CO2 are needed?

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For the reaction 

2H2S (g) + 3O2 (g) → 2H20 (l) + 2SO2 (g)  

ΔH° = -1124.0 kJ and ΔS° = -390.7 J/K 

The standard free energy change for the reaction of 1.91 moles of H2S(g) at 339 K, 1 atm would be ________ kJ.

This reaction is (reactant, product) _________ favored under standard conditions at 339 K.

Assume that ΔH° and ΔS° are independent of temperature.  

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For the reaction 

2HBr (g) → H2 (g) + Br2 (l) 

ΔG° = 104.8 kJ and ΔH° = 72.6 kJ at 281 K and 1 atm. 

This reaction is (reactant, product) _________  favored under standard conditions at 281 K.

The entropy change for the reaction of 1.80 moles of HBr(g) at this temperature would be________ J/K. 

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For the reaction 

2H2 (g) + O2 (g) → 2H2O (g) 

ΔG° = -455.6 kJ and ΔS° = -88.9 J/K at 315 K and 1 atm. 

This reaction is (reactant, product) _________  favored under standard conditions at 315 K.

The standard enthalpy change for the reaction of 2.47 moles of H2(g) at this temperature would be _________ kJ.

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For the reaction 

2CO (g) + 2NO (g) → 2CO2 (g) + N2 (g) 

ΔH° = -746.6 kJ and Δ S° = -198.0 J/K 

The standard free energy change for the reaction of 1.80 moles of CO(g) at 258 K, 1 atm would be _______ kJ.

This reaction is (reactant, product) ________ favored under standard conditions at 258 K.

Assume that ΔH° and ΔS° are independent of temperature. 

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How many photons are produced in a laser pulse of 0.580 J at 637 nm?

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You may want to reference ( page) section 5.6 while completing this problem.

A gas mixture with a total pressure of 700 mmHg contains each of the following gases at the indicated partial pressure: 126 mmHg CO2, 220 mmHg Ar and 188 mmHg O2. The mixture also contain helium gas.

Part B

What mass of helium gas is present in a 12.6 L sample of this mixture at 274 K?

Express your answer in grams.

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Microwave ovens emit microwave energy with a wavelength of 13.0 cm. What is the energy of exactly one photon of this microwave radiation? 

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You may want to reference ( page) section 5.6 while completing this problem.

A gas mixture with a total pressure of 700 mmHg contains each of the following gases at the indicated partial pressure: 126 mmHg CO2, 220 mmHg Ar and 188 mmHg O2. The mixture also contain helium gas.

Part A

What is the partial pressure of the helium gas.

Express your answer in millimeters of mercury.

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A wine-dispensing system uses argon canisters to pressurize and preserve wine in the bottle. An argon canister for the system has a volume of 56.8 mL and contains 30.0 g of argon.

Part A

An Assuming ideal gas behaviour, what is the pressure in the canister at 306 K? 

Express your answer with the appropriate units. 

Part B 

When the argon is released from the canister it expands to fill the wine bottle. How many 780.0-mL wine botles can be purged with the argon in the canister at a pressure of 1,46 atm and a temperature of 306 K ? 

Express your answer as an integer. 

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Calculate the wavelength of light produced if an electron moves from n = 5 state to n = 3 state of an electron in a hydrogen atom.

Express your answer to three significant figures and include the appropriate units. 

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In glycolysis, the reaction of glucose (Glu) to form glucose-6-phosphate (G6P) requires ATP to be present as described by the following equation: 

Glu + ATP → G6P + ADP        ΔG°298 = -17 kJ

In this process, ATP becomes ADP summarized by the following equation: 

ATP → ADP      ΔG°298 = -30 kJ

Determine the standard free energy change for the following reaction, and explain why ATP is necessary to drive this process:

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For the following reaction, 20.1 grams of iron are allowed to react with 42.3 grams of chlorine gas.

iron (s) + chlorine (g) → iron(III) chloride(s) 

What is the maximum mass of iron(III) chloride that can be formed? 

What is the FORMULA for the limiting reagent? 

What mass of the excess reagent remains after the reaction is complete? 

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For the following reaction, 0.182 moles of aluminum oxide are mixed with 0.268 moles of sulfuric acid. 

aluminum oxide (s) + sulfuric acid (aq) → aluminum sulfate (aq) + water(l) 

What is the formula for the limiting reagent? 

What is the maximum amount of aluminum sulfate that can be produced?

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For the following reaction, 0.266 moles of hydrogen gas are mixed with 0.452 moles of iodine. 

hydrogen (g) + iodine (s) → hydrogen iodide (g) 

What is the formula for the limiting reagent? 

What is the maximum amount of hydrogen iodide that can be produced? 

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