Question 1 Which of the equations below corresponds to the standard molar enthal

Question

Question 1 Which of the equations below corresponds to the standard molar enthalpy of formation for AgNO3, DHf(AgNO3)?

1. Ag (s) + 1/2 N2 (g) + 3/2 O2 (g) -> AgNO3 (s)

2. 2 Ag (s) + N2 (g) + 3 O2 (g) -> 2 AgNO3 (s)

3. Ag (s) + N (g) + O3 (g) -> AgNO3 (s)

4. Ag+1 (aq) + NO3-1 (aq) -> AgNO3 (s)

Question 2 50.0 calories of heat is supplied to a piece of gold of unknown mass. The temperature of the gold ingot raises 15.4 °C. What is the mass of the gold ingot in grams? Specific Heat(Au) = 0.0310 cal/gÝ°C

1. 9.55 ´ 10-3 g

2. 0.101 g

3. 23.9 g

4. 9.94 g

5. 105 g

Question 3 How much heat must be added to a 4.33 g piece of aluminum to raise its temperature from 22.00 °C to 27.00 °C? Specific Heat(Al) = 0.900 J/gÝK

1. 15.2 J

2. 19.5 J

3. 22.8 J

4. 6.88 J

5. none of these

Question 4 Given the following two equations and their corresponding enthalpies: CO (g) + 1/2 O2 (g) -> CO2 (g) DH1 = -283.0 kJ N2 (g) + O2 (g) -> 2 NO (g) DH2 = 180.6 kJ What is the enthalpy of reaction DHrxn for the reaction that follows? CO (g) + NO (g) -> CO2 (g) + 1/2 N2 (g) DHnet rxn = ??

1. DHrxn = -373.3 kJ

2. DHrxn = -385.4 kJ

3. DHrxn = -746.6 kJ

4. DHrxn = -192.7 kJ

5. DHrxn = -102.4 kJ

Question 5 Liquid hydrogen peroxide is an oxidizing agent in many rocket fuel mixtures because it releases oxygen gas on decomposition as shown below. 2 H2O2 (mc016-1.jpg ) -> 2 H2O (mc016-2.jpg ) + O2 (g) DHrxn = -196 kJ How much heat is released when 25.0 grams of H2O2 decomposes? Molar Mass(H2O2) = 34.01 g/mol

1. -133 kJ

2. -533 kJ

3. -144 kJ

4. -72.0 kJ

5. -288 kJ

Question 6 Given the equation below, what is DH for burning 2.00 g of CO (g) in excess oxygen? 2 CO (g) + O2 (g) -> 2 CO2 (g) DH = -566 kJ

1. none of these

2. -40.4 kJ

3. -10.1 kJ

4. -20.2 kJ

5. -28.4 kJ

Question 7 Which of the following reactions absorbs heat from the surroundings in order to proceed to completion?I. CO (g) + 1/2 O2 (g) -> CO2 (g) DHrxn = -283.0 kJ II. Al2O3 (s) -> 2 Al (s) + 3/2 O2 (g) (endothermic) III. SO3 (g) + 99.2 kJ -> S (s) + 3/2 O2 (g)

1. I and III

2. All of these

3. I only

4. II and III

5. I and II

Question 8 Given the following experimental data: DHrxn Ca (s) + 2 H2O (mc078-1.jpg ) -> Ca(OH)2 (s) + H2 (g) -415.1 kJ 1/2 H2 (g) + 1/2 Cl2 -> HCl (g) -92.31 kJ CaCl2 (s) + 2 H2O (mc078-2.jpg ) -> Ca(OH)2 (s) + 2 HCl (g) 195.3 kJ What is the standard heat of formation (DHf) for CaCl2 (s)?

1. +702.6 kJ/mol

2. +127.5 kJ/mol

3. -116.8 kJ/mol

4. -797.0 kJ/mol

5. -311.3 kJ/mol

Question 9 What is the enthalpy of reaction DH°rxn for the following reaction? SiO2 (s) + 4 HF (g) -> SiF4 (g) + 2 H2O (mc076-1.jpg ) DH°rxn = ?? DH°f(SiO2) = -910.9 kJ/mol DH°f(HF) = -273.0 kJ/mol DH°f(SiF4) = -1614.9 kJ/mol DH°f(H2O) = -285.8 kJ/mol

1. -1002.6 kJ/mol

2. -183.6 kJ/mol

3. -3084.6 kJ/mol

4. -716.8 kJ/mol

5. -4189.4 kJ/mol

Question 10 Which of the following reactions releases heat to the surroundings as it proceeds to completion? I. C (coal) + H2O (g) + 130 KJ -> CO (g) + H2 (g) II. 2 NO2 (g) -> N2O4 (exothermic) III. 2 H2 (g) + O2 (g) -> 2 H2O (g) DHrxn = -572 kJ

1. II and III

2. I and III

3. I only

4. I and II

5. All of these

Explanation / Answer

Question 1) Answer 1 because the delta H of formation of each of the reactants is zero (They're all elements in their natural state).

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Question 2)

q = m*Cs*?T

50 cal = m * (0.0310 cal g-1oC-1) * (15.4 oC)

Solving for m = 104.733 = 105 g, so answer 5

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Question 3)

Same equation as question 2.

q = m * Cs * (Tf - Ti)

q = 4.33 g * (0.900 J / g K) * (27 -22) = 19.485 which is answer 2.

*Note that one degree change in Kelvin is the same as one degree change in Celsius. No unit conversion necessary.

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Question 4)

Answer 1, which is -373.3 kJ.

You leave the first reaction alone, so its delta H value is -283 kJ still. The second reaction you must flip and then divide by two. So change the sign of the delta H value and divide by two: -90.3 kJ. Summing the delta H values gives -373.3 kJ

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Question 5)

25 g H2O2 * (1 mol / 34 g) * (196 kJ released / 1 mol) = 144 kJ released = -144 kJ (answer 3)

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Question 6)

Molar mass of CO = 28 g / mol

2.00 g * (1 mol / 28 g) * ( -566 kJ / 2 mol CO) = -20.2 kJ (answer 4)

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Question 7)

Answer 4.

II and III have heat in the reactants side (endothermic reaction).

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Question 8)

Answer 4. Similar to question 4. Flip the reactions and multiply them as needed to get the reaction you desire.

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Question 9)

Sum delta H values of products, then sum delta H values of reactants. Subtract the sum of products from reactants. Ensure you mutliply the appropriate delta H values by reaction coefficients.

Answer 2, which is -183.6 kJ.

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Question 10)

Answer 1. II and III are exothermic reactions (heat on the product side).

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