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Exam 8: Thermodynamics: the First Law

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Question 1

Multiple Choice

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At constant pressure and temperature,which of the following statements is true for the reaction: N₂O₅(s)  2NO₂(g) + ½O₂(g) ,H_r = 109.5 kJmol^1 at 298 K.

A) (H is independent of the physical states of the reactants.)
B) (H = U)
C) w = 0
D) (H < U)
E) (H > U)

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Question 2

Multiple Choice

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When nitrogen gas expands from 3.00 to 6.00 L and 2.00 kJ of energy is transferred as heat to the nitrogen in a cylinder fitted with a piston at an external pressure of 2.00 atm,against this constant pressure,what is U for the process?

A) (0.608 kJ)
B) +2.61 kJ
C) (2.61 kJ)
D) 0
E) +1.39 kJ

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Question 3

Multiple Choice

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What type of process is the formation of solid magnesium chloride from a gas of its ions?

All bond enthalpies are positive.True or false?

Calculate the enthalpy change that occurs when 1 lb (454 g) of mercury freezes at its freezing point (234.3 K) .The standard enthalpy of fusion of mercury is 2.29 kJmol^1.

A battery does 35 kJ of work driving an electric motor and 7 kJ of heat are released.What is the change in internal energy of the system?

If 2.00 mol of an ideal gas at 300 K and 3.00 atm expands from 6.00 L to 18.00 L and has a final pressure of 1.20 atm,isothermally and reversibly,which of the following is correct?

Match the values with the correct enthalpy change. Enthalpy Value H_f(C(g)) 1300 kJmol^1 H_f(C(s),(graphite)) +717 kJmol^1 H_c(C₂H₂(g)) +31 kJmol^1 H_f(Br₂(g)) 0

If the standard enthalpy of combustion of ethanol,C₂H₅OH(l) ,at 298 K is 1368 kJmol^1,what is the standard enthalpy of formation of ethanol? The standard enthalpies of formation of carbon dioxide and liquid water are 393.51 and 285.83 kJmol^1,respectively.

For Br₂(l),the standard enthalpy of formation is ______________________ (positive/ negative/ zero).

A closed system can exchange energy with the surroundings.True or false?

Calculate the standard enthalpy of formation of bicyco[1.1.0]butane (shown below) given the standard enthalpies of formation of C(g) and H(g) ,717 and 218 kJmol^-1,respectively,and the average C-H and C-C bond enthalpies,412 and 348 kJmol^-1,respectively.

Calculate the standard enthalpy of formation of potassium chloride given the following enthalpy data. K(s) K(g) +89 kJmol^1 K(g) K⁺(g)+ e^ +418 kJmol^1 ½Cl₂(g) Cl(g) +122 kJmol^1 Cl(g)e^  Cl^(g) 349 kJmol^1 KCl(s) K⁺(g)+ Cl^(g) +717 kJmol^1

For gaseous hydrogen atoms at 298 K is +217.kJmol^1,the standard enthalpy of formation can be best written as:

If an isolated system contained +5 kJ of energy,after 100 years U =

The temperature of a sample increases at its boiling point until all the liquid has been vaporized.True or false?

Calculate the final temperature when 2.50 kJ of energy is transferred as heat to 1.50 mol N₂ at 298 K and 1 atm at constant pressure.

What equation corresponds to the standard enthalpy of formation of gaseous hydrogen atoms,which,at 298 K is +217 kJmol^1?

For most reactions,the value of U is very close to that for H.True or false?

When a gas expands into a vacuum,w = 0.True or false?