Exam 5: Thermochemistry: Energy Changes in Reactions

When ammonium nitrate (NH₄NO₃)(s) is used in explosives, it decomposes to N₂(g), O₂(g), and H₂O(g). Write a balanced reaction equation for the decomposition of ammonium nitrate, and determine the standard enthalpy of reaction using standard enthalpies of formation: solid ammonium nitrate  366 kJ/mol and water vapor  242 kJ/mol.

Given the standard enthalpies of formation for the following substances, determine the reaction enthalpy for the following reaction. 2N₂H₄(g) 2NO₂(g) 3N₂(g) 4H₂O(g) H_rxn  ? kJ SubstanceH in kJ/mol N₂H₄(g)95.4 NO₂(g)33.1 H₂O(g)241.8

Which arrow in the following diagrams represents an endothermic phase transition?

Use the following information to determine the enthalpy for the reaction shown below. CH₄(g)  H₂O(g)  CO(g)  3H₂(g) H  ? 2C(s)  2H₂O(g)  CH₄(g)  CO₂(g) H  15.3 kJ C(s)  H₂O(g)  CO(g)  H₂(g) H  131.3 kJ CO(g)  H₂O(g)  CO₂(g)  H₂(g) H  41.2 kJ

Internal energy is defined as ________

Predict the temperature change produced by burning 3.55 g benzoic acid in a bomb calorimeter that has a heat capacity of 20.12 kJ/C. The enthalpy of combustion of benzoic acid is 26.43 kJ/g.

You hold a 50 g sphere of copper in one hand and a 25 g sphere of aluminum in the other hand. If both absorb energy at the same rate, which will come to your body temperature first and why? The specific heat capacities are 0.4 J/(g  ) for copper and 0.9 J/(g  ) for aluminum.

Which arrow in the following diagrams represents an exothermic phase transition?

Assuming that the distances between the two ions are the same in all cases, which of the following ion pairs has the smallest electrostatic potential energy (i.e., smallest in magnitude)?

In terms of the enthalpy of formation, which of the following compounds is most stable relative to its elements under standard conditions?

What is the heat capacity (C_p) of a 7.5 g piece of tin if its temperature changes by 12.3C when it is supplied with 20 J from a Bunsen burner?

Heat is best defined as ________

Fuel value is ________

Which of the following substances will release the most energy during combustion in air?

You have a summer job in a lead foundry. Your task is to identify how energy efficiency can be improved. You therefore need to know the minimum amount of energy it takes to raise 1 pound of lead (454 g) from room temperature (25 ) to its melting point (327 ) and then melt it. The specific heat capacity of lead is 0.159 J/(g  ), the enthalpy of fusion is 24.7 J/g, and the molar mass is 207 g/mol.

Which of the following bar charts shows the correct internal energy changes that occur in a pitcher of iced tea (system), the refrigerator (surroundings), and the universe as the iced tea in the refrigerator cools?

Which one of the following statements is not correct?

In an experiment, 10.0 g of ice at 20C is converted into steam with a temperature of 110 . How much energy is required for this process? _vap  2,260 J/g; H_fus  334 J/g; c_s(ice)  2.06 J/(g  ); c_s(water)  4.18 J/(g  ); c_s(steam)  1.99 J/(g  ))

When a 13.0 g sample of NaOH(s) dissolves in 400.0 mL of water to produce 413.0 g of solution in a constant pressure calorimeter, the temperature of the water and reaction vessel changes from 22.6C to 30.6C. Assume that the specific heat capacity of the solution is 4.20 J/(g  C), and that the heat capacity of the reaction vessel is 1.00 J/C. What is the molar enthalpy of solution of sodium hydroxide (40.00 g/mol)?

The cooling system in an automobile holds 10.0 L of ethylene glycol antifreeze. How much energy is absorbed when the temperature of the ethylene glycol goes from 20 to 100 ? The density and specific heat capacity of ethylene glycol are 1.11 g/mL and 2.42 J/(g  ), respectively.