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Exam 9: Thermochemistry Energy Changes in Chemical Reactions

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Question 41

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When 2.28 g of octane (molar mass = 114.23 g/mol) reacts with excess oxygen in a constant volume calorimeter, the temperature of the calorimeter increases by 20.0 $\degree$ C.The heat capacity of the calorimeter is 5.09 kJ/ $\degree$ C.Determine the energy flow, q_rxn, per mole of octane.

A) (-2 kJ)
B) (+5090 kJ)
C) (-102 kJ)
D) (-5090 kJ)
E) (-2.03 kJ)

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Question 42

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A Snickers bar contains 12 g fat, 33 g carbohydrates, and 4.0 g protein.Assuming that the food values of fat, carbohydrates, and protein are 9.0 Cal/g, 4.0 Cal/g, and 4.0 Cal/g, calculate approximately how many grams of water could be heated from 20.0 $\degree$ C to 100.0 $\degree$ C from the energy available from one bar.1 Cal = 4.184 kJ; c_p of water = 4.18 J/(g . $\degree$ C) )

A) 760 g
B) 150 g
C) 3200 g
D) 260 g
E) 3.2 g

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Question 43

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Calculate the work performed on/by a gas when it is compressed under a constant pressure of 8.00 atm from 95.0 L to 9.5 L.(101.3 J = 1 L.atm)

Which of the following hydrocarbons has the greatest fuel value?

Describe the difference between the change in the internal energy ( $\Delta$ E ) of a system and the change in enthalpy ( $\Delta$ H).Begin your description with the definition of enthalpy.

The freezing point of ammonia (NH₃, 17.04 g/mol) is -77.73 $\degree$ C.In an experiment, 367.2 grams of solid NH₃ at-77.73 $\degree$ C is used to cool 250.0 grams of liquid NH₃ from 25.00 $\degree$ C to the freezing point.Assume that the specific heat capacity of liquid NH₃ is 4.742 J/(g . $\degree$ C) .What is the enthalpy of fusion of ammonia?

A 19.5 g piece of titanium [c_p =0.523 J/(g . $\degree$ C) ] is heated and then submerged in 1.50 *10² grams of water [c_p = 4.18 J/(g . $\degree$ C) ] initially at 22.7 $\degree$ C.The final temperature comes to 23.7 $\degree$ C.What was the initial temperature of the Ti metal?

The kinetic energy associated with the random motion of molecules is called

A 1.20 kg piece of granite [c_p= 0.790 J/(g . $\degree$ C) ] at 60.0 $\degree$ C must be cooled to 24.0 $\degree$ C by submersion in water.How much water [c_p = 4.18 J/(g . $\degree$ C) ], initially at 18 $\degree$ C, would be required?

A food sample was burned in a bomb calorimeter containing 786 mL water.How much thermal energy was produced when the temperature of the water [c_v = 4.148 J/g . $\degree$ C) ] and the calorimeter rose from 20.00 $\degree$ C to 23.91 $\degree$ C? The metal calorimeter had a heat capacity of 1053 J/ $\degree$ C without the water.

A 65.0 g piece of chromium [c_p = 0.449 J/(g . $\degree$ C) ] is heated to a temperature of 120.0 $\degree$ C and then placed in contact with a 95.0 g piece of zinc at 20.0 $\degree$ C [c_p = 0.387 J/(g . $\degree$ C) ].What is the final temperature of the two pieces of metal?

Given 150 grams each of water and of gold, which requires more energy to raise its temperature by 80.0 $\degree$ C and by what factor? [Au: c_p = 0.129 J/(g . $\degree$ C) ; H₂O: c_p = 4.18 J/(g. $\degree$ C) ]

A sample of neon gas is contained in a cylinder fitted with a movable piston that has a mass of 0.580 kg.If the gas expands and pushes the piston out through a distance of 5.00 m with an acceleration of 11.5 ms-2, calculate w for the gas.F = ma, where F is force, m is mass, and a is acceleration.(1J =1 kg m²s ^{- 2} )

Which statement below regarding heat capacity is FALSE?

When solid NH₄NO₃ is dissolved in water, the temperature of the water and beaker gets noticeably colder.The formation of an aqueous solution of ammonium nitrate is

Which ionic compound below would you expect to have the highest solubility in water based on its lattice energy?

Which statement below regarding heating curves is FALSE?

In an experiment, 9.80 g of olive oil at 80.0 $\degree$ C are quickly transferred to water in a calorimeter at 18.0 $\degree$ C.The heat capacity of the calorimeter with the water is 212 J/ $\degree$ C.The final equilibrium temperature is 22.8 $\degree$ C.What is the approximate specific heat capacity of the olive oil?

The basal metabolic rate (BMR) is the minimum energy intake required to maintain a body that is awake and at rest.While the rate varies with age, gender, health, and body mass, a reasonable value is 1600 Cal per day.Walking can require 2.5 times the BMR.Using this information, calculate the energy expended by someone walking at a speed of 3.0 mph and determine how far she could walk with the energy from a quarter-pound hamburger 125 g) that has a food value of 3.6 Cal/g.

Thermochemistry is the study of how _______ is produced and consumed during chemical reactions.