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Exam 6: Energy Relationships in Chemical Reactions

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Question 31

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Ethanol undergoes combustion in oxygen to produce carbon dioxide gas and liquid water. The standard heat of combustion of ethanol, C₂H₅OH(l) , is -1366.8 kJ/mol. Given that $\Delta$ H°_f[CO₂(g) ] = -393.5 kJ/mol and $\Delta$ H°_f[H₂O(l) ] = -285.8 kJ/mol, what is the standard enthalpy of formation of ethanol?

A) 3,010 kJ/mol
B) -687.6 kJ/mol
C) -277.6 kJ/mol
D) 687.6 kJ/mol
E) 1,367 kJ/mol

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Question 32

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Methanol (CH₃OH) burns according to the equation 2CH₃OH(l) + 3O₂(g) $\rarr$ 2CO₂(g) + 4H₂O(l) , $\Delta$ H°_rxn = -1454 kJ/mol. How much heat, in kilojoules, is given off when 75.0 g of methanol is burned?

A) 727 kJ
B) 3.22 * 10³ kJ
C) 1.45 * 10³ kJ
D) 1.70 * 10^-3 kJ
E) 3.41 * 10³ kJ

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Question 33

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For the reaction C(graphite) + O₂(g) $\rarr$ CO₂(g) $\Delta$ H° = -393 kJ/mol How many grams of C(graphite) must be burned to release 275 kJ of heat?

Pentaborane B₅H₉(s) burns vigorously in O₂ to give B₂O₃(s) and H₂O(l) . Calculate $\Delta$ H°_rxn for the combustion of 1 mol of B₅H₉. $\Delta$ 0H°_f[B₂O₃(s) ] = -1,273.5 kJ/mol $\Delta$ H°_f[B₅H₉(s) ] = 73.2 kJ/mol $\Delta$ H°_f[H₂O(l) ] = -285.8 kJ/mol

A 26.2 g piece of copper metal is heated from 21.5°C to 201.6°C. Calculate the amount of heat absorbed by the metal. The specific heat of Cu is 0.385 J/g·°C.

The combustion of butane produces heat according to the equation 2C₄H₁₀(g) + 13O₂(g) $\rarr$ 0 8CO₂(g) + 10H₂O(l) $\Delta$ H°_rxn= -5,314 kJ/mol How many grams of butane must be burned to release 1.00 * 10⁴ kJ of heat?

The value of $\Delta$ H°_rxn for the following reaction is -6535 kJ/mol. 2C₆H₆(l)+ 15O₂(g) $\rarr$ 12CO₂(g)+ 6H₂O(g) How many kilojoules of heat will be evolved during the combustion of 16.0 g of C₆H₆(l)?

When 0.560 g of Na(s) reacts with excess F₂(g) to form NaF(s) , 13.8 kJ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation ( $\Delta$ H°_f) of NaF(s) ?

Potential energy is

Chemical energy is

At 25°C, the following heats of reaction are known: At the same temperature, use Hess's law to calculate $\Delta$ H°_rxn for the reaction: ClF(g) + F₂(g) $\rarr$ ClF₃(g)

The combustion of pentane produces heat according to the equation C₅H₁₂(l) + 8O₂(g) $\rarr$ 5CO₂(g) + 6H₂O(l) $\Delta$ H°_rxn= -3,510 kJ/mol How many grams of CO₂ are produced per 2.50 * 10³ kJ of heat released?

Solid sodium peroxide (Na₂O₂) reacts with liquid water yielding aqueous sodium hydroxide and oxygen gas. How much heat is released when 250.0 L of oxygen gas is produced from the reaction of sodium peroxide and water if the reaction is carried out in an open container at 1.000 atm pressure and 25°C? (Given: $\Delta$ H°_f[Na₂O₂(s) ] = -510.9 kJ/mol; $\Delta$ H°_f[NaOH(aq) ] = -469.2 kJ/mol; $\Delta$ H°_f[H₂O(l) ] = -285.8 kJ/mol)

Styrene, C₈H₈, is one of the substances used in the production of synthetic rubber. When styrene burns in oxygen to form carbon dioxide and liquid water under standard-state conditions at 25°C, 42.62 kJ are released per gram of styrene. Find the standard enthalpy of formation of styrene at 25°C. (Given: $\Delta$ H°_f[CO₂(g) ] = -393.5 kJ/mol, $\Delta$ H°_f[H₂O(l) ] = -285.8 kJ/mol, $\Delta$ H°_f[H₂O(g) ] = -241.8 kJ/mol)

Find $\Delta$ H°_rxn for the reaction CH₄(g)+ 2O₂(g) $\rarr$ CO₂(g)+ 2H₂O(l). [ $\Delta$ H°_f (CH₄(g))= -74.8 kJ/mol; $\Delta$ H°_f (CO₂(g))= -393.5 kJ/mol; $\Delta$ H°_f (H₂O(l))= -285.5 kJ/mol]

The heat absorbed by a system at constant pressure is equal to $\Delta$ E + P $\Delta$ V.

Given H₂(g) + (1/2) O₂(g) $\rarr$ H₂O(l) , $\Delta$ H° = -286 kJ/mol, determine the standard enthalpy change for the reaction 2H₂O(l) $\rarr$ 2H₂(g) + O₂(g) .

A 0.3423 g sample of pentane, C₅H₁₂, was burned in a bomb calorimeter. The temperature of the calorimeter and the 1.000 kg of water contained therein rose from 20.22°C to 22.82°C. The heat capacity of the calorimeter is 2.21 kJ/°C. The heat capacity of water = 4.184 J/g·°C. What is the heat of combustion, in kilojoules, per gram of pentane?

A gas is allowed to expand, at constant temperature, from a volume of 1.0 L to 10.1 L against an external pressure of 0.50 atm. If the gas absorbs 250 J of heat from the surroundings, what are the values of q, w, and $\Delta$ E?

The heat capacity of 20.0 g of water is 83.7 J/°C.