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Exam 6: Thermochemistry: Energy Flow and Chemical Change

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Question 31

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a.Define,or explain fully what is meant by the standard enthalpy of formation of a substance, $\Delta$ H°_f . b.What is the standard state of the element oxygen? c.Write down in full the formation reaction for liquid ethanol,C₂H₅OH(l).The equation should be balanced and should indicate the physical state of each substance.

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a.H°_f is the enthalpy change ...

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Question 32

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Which of the following is not a state function?

A) internal energy
B) volume
C) work
D) pressure
E) enthalpy

F) A) and C)
G) B) and E)

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Question 33

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$\Delta$ E values obtained by bomb calorimetry can be converted to give accurate $\Delta$ H values.

A piece of copper metal is initially at 100.0°C.It is dropped into a coffee cup calorimeter containing 50.0 g of water at a temperature of 20.0°C.After stirring,the final temperature of both copper and water is 25.0°C.Assuming no heat losses,and that the specific heat (capacity) of water is 4.18 J/(g·K) ,what is the heat capacity of the copper in J/K?

Calculate q when 28.6 g of water is heated from 22.0°C to 78.3°C.

A system delivers 1275 J of heat while the surroundings perform 855 J of work on it.Calculate $\Delta$ E in J.

Calculate,in J,the work done by 10.0 g of CO₂ when it sublimes against a pressure of 1.00 atm to form gaseous CO₂ at 0.0°C.The volume of CO₂(s)can be neglected;CO₂(g)can be assumed to behave ideally.The process occurring is CO₂(s) $\to$ CO₂(g)

A system that does no work but which receives heat from the surroundings has

Calculate the enthalpy change for the reaction NO(g) + O(g) $\to$ NO₂(g) From the following data:

a.Explain fully what is meant by the term "state function." b.(i)Give two examples of thermodynamic quantities which are state functions. (ii)Give two examples of thermodynamic quantities which are not state functions.

A system initially has an internal energy E of 501 J.It undergoes a process during which it releases 111 J of heat energy to the surroundings,and does work of 222 J.What is the final energy of the system,in J?

The enthalpy (H)of liquid water is greater than that of the same quantity of ice at the same temperature.

Calculate the $\Delta$ H°_rxn for the following reaction. $\Delta$ H°_f [AsH₃(g) ] = 66.4 kJ/mol; $\Delta$ H°_f [H₃AsO₄(aq) ] = -904.6 kJ/mol; $\Delta$ H°_f [H₂O(l) ] = -285.8 kJ/mol H₃AsO₄(aq) + 4H₂(g) $\to$ AsH₃(g) + 4H₂O(l)

An important step in the synthesis of nitric acid is the conversion of ammonia to nitric oxide. $\Delta$ H°_f [NH₃(g) ] = -45.9 kJ/mol; $\Delta$ H°_f [NO(g) ] = 90.3 kJ/mol; $\Delta$ H°_f [H₂O(g) ] = -241.8 kJ/mol 4NH₃(g) + 5O₂(g) $\to$ 4NO(g) + 6H₂O(g) Calculate $\Delta$ H°_rxn for this reaction.

The dissolution of barium hydroxide in water is an exothermic process.Which of the following statements is correct?

Clearly state the thermodynamic standard state of a.an element or compound. b.a solute.

For a reaction in a sealed,rigid container, $\Delta$ H is always greater than $\Delta$ E.

The reaction 2NaOH(aq)+ H₂SO₄(aq) $\to$ Na₂SO₄(aq)+ 2H₂O(l) was studied in a coffee cup calorimeter.100.mL portions of 1.00 M aqueous NaOH and H₂SO₄,each at 24.0°C,were mixed.The maximum temperature achieved was 30.6°C.Neglect the heat capacity of the cup and the thermometer,and assume that the solution of products has a density of exactly 1 g/mL and a specific heat capacity of 4.18 J/(g·K). a.Calculate the heat of reaction,q,in J. b.Calculate $\Delta$ H,the heat (enthalpy)of reaction,in kJ/mol of Na₂SO₄ produced.

When 1.00 g of solid NH₄Cl is dissolved in 25.00 g of water contained in a coffee cup calorimeter,both reagents initially being at 25.0°C,the temperature falls to 22.4°C.Assuming that the heat capacity of the ammonium chloride solution is 4.18 J/(g·K),calculate the heat (enthalpy)of solution of NH₄Cl, (a)in J/g and (b)in kJ/mol.

The standard heat (enthalpy)of formation of graphite is zero.