SB Week 7 HW Chap 6

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

Match each set of conditions with the type of compound when that compound is under standard conditions at a given temperature.

Gas → 1 atm Aqueous solution → 1 M Pure substance → Stable form at the given temperature and 1 atm of pressure

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

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

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 or standard state atm, bar, or atmosphere M, molar, mole/liter, mol/L, or mole per liter

Energy transferred when an object is moved by a force results in ________ being done on that object.

work

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)

In a thermochemical equation, the _____ change is always written next to the balanced chemical equation.

enthalpy

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 q= c*mass*ΔT 3.56g(1 kg/1000 g)(1 kJ/ 1 kg) q= 0.385 J/g*K*0.00356 kJ*304.5 °C

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. Compound ΔH°f (kJ/mol) HF (g) -273.0 H2O (l) -285.8 SiF4 (g) -1614.9 SiO2 (s) -910.9

-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 q= c*mass*ΔT (2 J/g⋅K)(10°C)(10g)= 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

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 w= -P△V .870L - .200L= .670 L 1.30 atm * 101.3 J= 131.69 -131.69*.670= -88.2 J

Calculate ΔH°rxn for the reaction A + 2B → 2C using the ΔH°f values given below. Compound ΔH°f A a B b C c

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.

21 °C q= c*mass*ΔT ΔT= q/c*mass 553J / (0.13 J/g⋅K)(84g) =50.64 ΔT= T(final)-T(initial) T(final)= T(initial)-ΔT 72 °C - 50.64°C = 21.36

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)

2H2(g) + 2Cl2 (g) → 4HCl (g)2H2(�) + 2Cl2 (�) → 4HCl (�) 2H2O(g) → O2 (g) + 2H2 (g)

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

What is the net equation when the following reactions are summed? 2C(graphite) + 3H2 (g) → C2H6 (g) C2H4 (g) → 2C(graphite) + 2H2 (g)

C2H4 (g) + H2 (g) → C2H6 (g)

Which of the following are state functions? Select all that apply.

Checking account balance Change in altitude ΔE

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)

Which of the following symbols is used to indicate internal energy?

E

True or false: If an ice cube is placed on a hot stove, heat transfers from the ice cube to the stove.

False

For a reaction that proceeds through a series of steps, ΔHoverall = ΔH1+ ΔH2+ ΔH3... This is a restatement of _____ law.

Hess's

The units for the molar heat capacity are _____.

J/mol⋅K

Which of the following are state functions? Select all that apply.

Mass Pressure Temperature

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.

NaCl AgCH3COO

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 is exothermic. The surroundings near Reaction 1 will become colder as it proceeds. Reaction 2 releases twice as much energy as Reaction 1 absorbs.

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 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. The arrow in the enthalpy diagram points from reactants to products. In an endothermic reaction, the reactants will be at the bottom of the enthalpy diagram.

Which of the following experimental values are used to solve for the specific heat capacity of a substance? Select all that apply.

The mass of the substance The heat absorbed or released (q) The temperature change

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

Which of the following statements correctly describe exothermic and endothermic reactions? Select all that apply.

The reactants in an endothermic reaction are lower in energy than the products. An exothermic reaction is one that releases heat to its surroundings. If the container of a reaction becomes colder during the reaction, the reaction is endothermic.

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 table underneath the mug The mug The air in the room

Which of the following statements correctly describe specific heat capacity (c)? Select all that apply.

The units of specific heat are J/g⋅K. The specific heat for a substance has the same value regardless of the size of the sample. The symbol for specific heat is c.

Which of the following statements correctly describe the relationship between the volume of a chemical system and work? Select all that apply.

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. The expansion of a gas can provide mechanical work.

The first law of thermodynamics states that the total amount of _____ in the universe remains constant.

energy

True or false: Both heat and work can be measured in joules.

True

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 _____ .

c heat, energy, thermal energy, or heat energy 1 or one K, Kelvin, C, Celsius, celsius, kelvin, degree celsius, or degree C

Use the equation for specific heat capacity to determine the function needed to solve for the variables associated with temperature change. Heat Mass of a substance Change in temperature Specific heat capacity

c × mass x ΔT q/c×ΔT q/mass×c q/mass×ΔT

A thermochemical equation links a reaction's stoichiometry to its _____ change or ΔHrxn.

enthalpy

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

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.

he initial temperature of the water The mass of the water in the cup The mass of the solid The final temperature of the system The initial temperature of the solid

The total change in the internal energy of a system is the sum of the energy transferred as _________ and/or __________.

heat, heat exchanged, or heat exchange work or work done

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

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

A constant _____ calorimeter is most frequently used to measure ΔH for a reaction in aqueous solution, whereas a constant _____ calorimeter is usually used to measure the heat of a combustion reaction.

pressure; volume

The symbol _____ always indicates heat (or thermal energy), which is transfered 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.

q(solid) → csolid × masssolid × ΔTsolid -qsolid → qwater csolid → -qwatermasssolid×ΔTsolid

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. term-51Which of the following options correctly reflect the steps required to calculate the molar heat of combustion of methanol? Select all that apply.

q/cal = +43.6 kJ The molar heat of combustion for methanol is -727 kJ/mol.

A _____ function is path independent, meaning that only the initial and _____ conditions are needed to measure the net change that occurred.

state final, ending, end, or current

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

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 w = -PΔV 2.75L - 5.42= ΔV 748 torr*(1 atm/760 torr)(1 J/101.3 atm)= P