SB Chapter 6
An experiment is developed to determine the energy change during a precipitation reaction, represented by the following balanced equation: AgCH3COO (aq) + NaCl (aq) → NaCH3COO (aq) + AgCl (s) Which of the following are part of the system? Select all that apply.
AgCH3COO NaCl
Which of the following is the correct enthalpy diagram for the decomposition of dinitrogen pentoxide, represented by the balanced equation 2N2O5 (g) + 447.4 kJ → 4NO (g) + 3O2 (g)?
B
Based on the first law of thermodynamics, the energy gained by a system is _____ the energy lost by the surroundings.
equal to
When ΔH for a thermochemical equation is negative, that reaction is _____, while a positive value for ΔH is associated with an _____ reaction.
exothermic; endothermic
True or false: If an ice cube is placed on a hot stove, heat transfers from the ice cube to the stove.
false
True or false: Both heat and work can be measured in joules.
true
Energy transferred when an object is moved by a force results in being done on that object.
work
Match each type of energy change with its associated symbol.
work = w heat = q internal energy = E
Consider the following reactions: A → 2B; ΔH = x kJ B → C; ΔH = y kJ What would be the enthalpy change associated with the reaction below? A → 2C
x + 2y
A combustion reaction known to generate x kJ of heat is measured in a constant volume (bomb) calorimeter. If the calorimeter is observed to change from Ti oC to Tf oC, what is the heat capacity of the entire calorimeter (in kJ/K)?
x/Tf-Ti
Which of the following relationships are true? Select all that apply.
ΔE = q + w (under any conditions) ΔE = ΔH + w (at constant P) ΔH = q (at constant P)
Match each type of calorimeter with the thermochemical property that it measures. Instructions
ΔH = Constant pressure (coffee cup) calorimeter ΔE = Bomb (constant volume) calorimeter
Match each thermodynamic symbol with its correct definition. Instructions
ΔHrxn = The change in enthalpy for a given reaction ΔHorxn = The enthalpy change of a reaction measured at the standard state ΔHof = The enthalpy change when 1 mol of a compound forms from its elements in their standard states
A thermochemical equation links a reaction's stoichiometry to its change or ΔHrxn.
enthalpy
In a thermochemical equation, the _____ change is always written next to the balanced chemical equation.
enthalpy
ΔE indicates a(n) in the internal energy of a system.
change
A 3.56-g piece of copper metal is heated from 20.5°C to 325°C. Calculate the heat absorbed (in kJ) by the metal if the specific heat of copper is 0.385 J/g⋅K. (Don't forget that ΔT will be the same numeric value either in K or °C units, since their degree size is equal. This would not be true for °F whose degree increment is smaller.)
+0.417 kJ
Hydrogen reacts with oxygen according to the following balanced thermochemical equation: 2H2 (g) + O2 (g) → 2H2O (l); ΔH = -572 kJ Given this information, what would be the enthalpy change associated with the following reaction? H2O (l) → H2 (g) + 1212O2 (g)
+286 kJ
Hydrogen reacts with oxygen according to the following balanced thermochemical equation: 2H2 (g) + O2 (g) → 2H2O (l); ΔH = -572 kJ Given this information, what would be the enthalpy change associated with the following reaction? H2O (l) → H2 (g) + 1212O2 (g) Multiple choice question.
+286 kJ
A 10.0-gram mineral sample is heated to 80.0oC and immersed in a constant pressure calorimeter containing 50.0 grams of water (cwater = 4.184 J/g⋅K) initially at 20.0oC. After heat exchange, the temperature of the calorimeter is 30.0oC. Calculate the heat capacity of the mineral (in J/g⋅K), assuming that all of the heat was exchanged with the water.
+4.18
Specific heat capacities are tabulated in units of J/g⋅K, but most temperature measurements are made in units of Celsius. If a system is initially at 5°C and is heated to 10°C, what is the change in temperature in kelvins?
+5
Calculate the standard enthalpy change for the reaction SiO2 (s) + 4HF (g) → SiF4 (g) + 2H2O (l) given the information in the table below.
-183.6 kJ
If an exothermic reaction heats a calorimeter with a total mass of 10 grams from 20°C to 30°C what is the total enthalpy change for the reaction? Assume that the specific heat capacity of the system is 2 J/g⋅K.
-200 J
A solid initially at 75°C is placed in an insulated water bath initially at 30°C. The temperature reaches 45°C. The change in temperature of the solid was _____ °C, and the change in temperature of the water bath was _____ °C. (Be careful with plus and minus signs.)
-30.°C; +15°C
By definition, the standard enthalpy of formation of a pure in its standard state is equal to 0 kJ/mol.
element
A reaction takes place in a piston-cylinder apparatus at constant temperature. The initial volume of the cylinder is 0.200 L and the final volume is 0.870 L. Calculate the work done in joules if the piston expanded against a constant external pressure of 1.30 atm. (1 atm⋅L = 101.3 J)
-88.2 J
32 g of ZnS reacts according to the balanced equation 2ZnS (s) + 3O2 (g) → 2ZnO (s) + 2SO2 (g); ΔH = -879 kJ. Select all the options that correctly reflect parameters that can be derived from the information given.
0.328 mol of ZnS reacts. This reaction releases 144 kJ of energy. 15.8 g of O2 are required to react completely with the ZnS present.
Match each energy unit with its equivalent in joules. Instructions
1 cal = 4.184 J 1 Btu = 1055 J 1 nutritional Calorie = 4184 J
Which of the following reactions is associated with the standard enthalpy of formation of NH3 (g)?
1/2N2 (g) + 3/2H2 (g) → NH3 (g)
Given the following thermochemical equations: 3A → 2B; ΔH = x kJ C → B; ΔH = y kJ What would be the total enthalpy change when the following reactions are summed to yield 3232A → C?
1/2x - y
The standard enthalpy of formation of a compound is the enthalpy change associated with the reaction that generates mole(s) of that compound from its component when all of the substances are under conditions.
1; elements; standard
Calculate ΔH°rxn for the reaction A + 2B → 2C using the ΔH°f values given below.
2(c) - (a) - 2(b)
84 g of a metal at an initial temperature of 72°C releases 553 J of heat. Calculate the final temperature of the metal if its specific heat capacity is 0.13 J/g⋅K.
21ºC
Consider the following formation reactions. 12O2 (g) +H2 (g) → H2O(g)12O2 (�) + H2 (�) → H2O(�) 12H2(g) +12Cl2 (g) → HCl (g)12H2(�) + 12Cl2 (�) → HCl (�) Using Hess's law, select the correct forms of the formation equations that will add up to the reaction below. 2H2O(g) +2Cl2 (g) → O2 (g) +4HCl (g)
2H2O(g) → O2 (g) +2H2 (g)2H2O(�) → O2 (�) + 2H2 (�) 2H2(g) + 2Cl2 (g) → 4HCl (g)
What is the net equation when the following reactions are summed? 2C(graphite) + 3H2 (g) → C2H6 (g) C2H4 (g) → 2C(graphite) + 2H2 (g)
2H4 (g) + H2 (g) → C2H6 (g)
Consider the following reactions: 2A → B; ΔH = x 2B → C; ΔH = y What is the total enthalpy change for the reaction 4A → C?
2x + y
Match the two figures (A and B) correctly with the terms "exothermic" and "endothermic." Instructions
A = exothermic B = endothermic
Which of the following changes in energy would be assigned a negative value in a thermochemical equation? Select all that apply.
A compressed spring is allowed to uncoil. A hot rock cools at sunset.
The internal energy change for a reaction is related to enthalpy by equation ΔE = ΔH - PΔV. This equation tells us that ΔH is very close to ΔE if there is no volume change in the reaction. In which of the following situations would ΔH give a good approximation of ΔE? Select all that apply.
A reaction involving only solids and liquids A reaction in which the change in the number of moles of gas present is zero
Which of the following options correctly define a state function? Select all that apply.
A state function is a quantity that does not depend on the path taken to achieve it. A state function is one that depends on the initial state of the system.
To generate the overall equation A → 2C, which two equations should be added together?
A → B B → 2C
Match each unit symbol with its name. Instructions
C = Kilocalorie cal = Calorie Btu = British thermal unit
Which of the following reactions would have an enthalpy change equal to ΔHfo? Select all that apply.
C(graphite) + O2 (g) → CO2 (g) Fe (s) + 3232Cl2 (g) → FeCl3 (s)
Which of the following are state functions? Select all that apply.
Change in altitude Checking account balance ΔE
The term _____ indicates that heat is absorbed by the system from the surroundings, while _____ indicates that heat is released by the system into the surroundings.
endothermic; exothermic
A salt is dissolved in a bath of water. Calculate the total amount of heat taken in or given out by the system (in J) if the temperature of mwater grams of water decreases from Ti oC to Tf oC when msalt grams of salt is added to it. Assume the specific heat capacity of the solution is Cs J/g⋅K. (Hint: consider the total mass of the solution.)
Cs⋅(mwater + msalt)⋅(Tf - Ti)
Match each set of conditions with the type of compound when that compound is under standard conditions at a given temperature. Instructions
Cs⋅(mwater + msalt)⋅(Tf - Ti)
Two equations must be manipulated in order to generate the overall equation A + 2B → D. Select the two chemical equations from below that can be arranged and added together to generate the overall equation. (Note: the equation(s) may need to be reversed or multiplied by a constant.)
D → C + B A + B → C
Which of the following symbols is used to indicate internal energy?
E
If there is a change in internal energy, ΔE, which of the following expressions could be used to calculate this? Select all that apply.
Eproducts - Ereactants Efinal - Einitial
Use the equation for specific heat capacity to determine the function needed to solve for the variables associated with temperature change. Instructions
Heat = c × mass x ΔT Mass of substance = qc×ΔT��×Δ� Change in temperature = qmass×c�mass×� Specific heat capacity= qmass×ΔT
For a reaction that proceeds through a series of steps, ΔHoverall = ΔH1+ ΔH2+ ΔH3... This is a restatement of law.
Hess
Which of the following substances would have a standard enthalpy of formation equal to 0 kJ/mol? Select all that apply.
Hg (l) H2 (g) Ar (g)
Which of the following statements correctly describe exothermic and endothermic reactions? Select all that apply.
If the container of a reaction becomes colder during the reaction, the reaction is endothermic. The reactants in an endothermic reaction are lower in energy than the products. An exothermic reaction is one that releases heat to its surroundings.
The units for the molar heat capacity are _____.
J/mol⋅K
Generate the equation A + 2B → 2D from a combination of the reactions provided. Reaction 1: A + 2B → 2C Reaction 2: C → D How must reactions 1 and 2 be combined to sum to the overall reaction?
Reaction 1 + 2(Reaction 2)
CO (g) can be produced by the reaction of coal with steam, as shown by the balanced equation: H2O (g) + C (s) → CO (g) + H2 (g). Which of the following options correctly reflect the steps required to calculate ΔH for this reaction, given the information shown below? Select all that apply. Reaction 1: H2 (g) + 1212O2 (g) → H2O (g); ΔH = -242.0 kJ Reaction 2: 2CO (g) → 2C (s) + O2 (g) ; ΔH = +221.0 kJ
Reaction 2 must be reversed and divided by 2. ΔH = +131.5 kJ
Which of the following statements correctly describe the two reactions outlined below? Select all that apply. Reaction 1: A → B ΔH = +50 kJ Reaction 2: C → D ΔH = -100 kJ
Reaction 2 releases twice as much energy as Reaction 1 absorbs. The surroundings near Reaction 1 will become colder as it proceeds. Reaction 2 is exothermic.
Match the effects of the following combinations of Reactions 1 and 2 with the reaction resulting from these combinations. Reaction 1: A → 2C Reaction 2: C → B
Rxn 1 + (-Rxn 2) =A + B -> 3C Rxn 1 + 2(Rxn 2) = A -> 2B (-Rxn 1) + (-Rxn 2) = B + C -> A
Which of the following are state functions? Select all that apply.
Temperature Mass Pressure
Which of the following options describe an enthalpy diagram correctly? Select all that apply.
The direction of the arrow in an enthalpy diagram indicates whether a reaction is exothermic or endothermic. Enthalpy, H, increases up the y-axis. In an endothermic reaction, the reactants will be at the bottom of the enthalpy diagram. The arrow in the enthalpy diagram points from reactants to products.
Which of the following statements correctly describe the relationship between the volume of a chemical system and work? Select all that apply.
The expansion of a gas can provide mechanical work. The work done by an expanding gas is calculated using the equation w = -PΔV. A chemical system may do work by the expansion of one or more gaseous products.
Which of the following experimental values are used to solve for the specific heat capacity of a substance? Select all that apply.
The heat absorbed or released (q) The temperature change The mass of the substance
Which of the following values are needed to solve for the heat capacity of a heated unknown solid when it is placed in a coffee cup calorimeter? Select all that apply.
The initial temperature of the solid The mass of the solid The final temperature of the system The initial temperature of the water The mass of the water in the cup
A 1.922-g sample of methanol (CH3OH; molar mass 32.04 g/mol) is burned in a constant-volume bomb calorimeter. The temperature of the water in the calorimeter rises from 23.51°C to 27.70°C. The heat capacity of the calorimeter plus water is given by 10.4 kJ/°C. Which of the following options correctly reflect the steps required to calculate the molar heat of combustion of methanol? Select all that apply.
The molar heat of combustion for methanol is -727 kJ/mol. qcal = +43.6 kJ
Select all that apply Hot coffee is poured into a mug. It slowly cools, releasing heat to the environment. If we consider the coffee to be the system, which of the following are part of the surroundings? Select all that apply.
The mug The air in the room The table underneath the mug
Which of the following statements correctly describe specific heat capacity (c)? Select all that apply.
The specific heat for a substance has the same value regardless of the size of the sample. The units of specific heat are J/g⋅K. The symbol for specific heat is c.
32 g of ZnS reacts according to the balanced equation 2ZnS (s) + 3O2 (g) → 2ZnO (s) + 2SO2 (g); ΔH = -879 kJ. Select all the options that correctly reflect parameters that can be derived from the information given.
This reaction releases 144 kJ of energy. 0.328 mol of ZnS reacts. 15.8 g of O2 are required to react completely with the ZnS present.
The first law of thermodynamics states that the total amount of in the universe remains constant.
energy
If a system gains heat as it does work on its surroundings, the total change in internal energy will _____.
be positive, negative, or zero
The specific heat capacity, abbreviated with the letter , is the quantity of required to change the temperature of gram of an object by 1 .An unknown solid is placed in a freezer until it reaches a constant temperature. It is then placed in a room temperature water bath. Identify the sign (+/-) of the temperature change for the solid and for the water bath. Instructions
c; heat; 1; C
Two solids of identical mass, A and B, are analyzed using identical calorimeters. Each calorimeter contains the same amount of water and is at room temperature. When the solids are heated to the same initial temperature and placed in their calorimeters, the final temperature of solid A's calorimeter is higher than that of B. What can we infer from this?
csolid A > csolid B
ΔH will be equal to ΔE if the total number of moles of does not change during a chemical reaction (discounting any small volume change caused by liquids or solids).ΔH will be equal to ΔE if the total number of moles of does not change during a chemical reaction (discounting any small volume change caused by liquids or solids).
gas
The total change in the internal energy of a system is the sum of the energy transferred as and/or .
heat; work
In the enthalpy diagram shown, the reactants are _____ in energy than the products. The reaction therefore _____ heat and is _____.
higher; releases; exothermic
The sum of all the potential and kinetic energies for all particles in a system is called the total energy (E) of the system.
internal
The SI unit of energy is the , which is abbreviated by the symbol .
joule J
The heat capacity of a substance is the amount of heat needed to change the temperature of 1 mol of that substance by K.
molar; 1
If heat is transferred from a system to its surroundings and the surroundings do work on the system, the sign of q will be _____, and the sign of w will be _____.
negative; positive
The change in enthalpy (ΔH) is equal to the change in heat (q) when the system is at constant _____.
pressure
Work may be done in a chemical system by a change in volume as a gaseous component expands or contracts at constant .
pressure
The symbol _____ always indicates heat (or thermal energy), which is transferred as a result of a difference in temperature between a system and its surroundings.
q
Match the variables associated with constant pressure calorimetry with their equivalent expressions. Instructions
qsolid = csolid×masssolid× ΔTsolid -qsolid = qwater csolid = -qwater/masssolid×ΔTsolid
Thermodynamic parameters are usually calculated for compounds under conditions, since values tend to vary somewhat with conditions. To be in this state, a gas must have a pressure of 1 , and a solution must have a concentration of 1 .
standard; atm; M
A function is path independent, meaning that only the initial and conditions are needed to measure the net change that occurred.
state; final
When calculating the temperature change for a reaction, a change of 1°C is _______.
the same as a change of 1 K
Hess's law states that the enthalpy change for an overall process is equal to _____.
the sum of the enthalpy changes for the individual steps
The study of heat changes in chemical reactions is called
thermochemistry
The study of energy and its transformations is called ______.
thermodynamics
An unknown solid is placed in a freezer until it reaches a constant temperature. It is then placed in a room temperature water bath. Identify the sign (+/-) of the temperature change for the solid and for the water bath. Instructions
ΔTsolid = Positive ΔTwater bath = Negative
A gas is compressed from a volume of 5.42 L to a volume of 2.75 L by an external pressure of 748 torr. Which of the following correctly reflect the calculations required to determine the work done on/by the system (the gas)? Select all that apply. 1 atm⋅L = 101.3 J and 1 atm = 760 torr
ΔV = -2.67 L w = 266 J
