Thermodynamics Reading
Calculate the heat capacity of a given calorimeter if combustion of a 1.000-gram sample of biphenyl, (C6H5)2, releases 21.78 kJ of heat together with a 2.94 °C temperature rise. 1.35 × 10-4 J/°C 7.41 × 103 J/°C 7.41 J/°C 1.35 × 10-1 J/°C
7.41 × 103 J/°C
In which of the following systems would the energy change be associated with a negative sign?
A compressed spring (the system) is allowed to uncoil. A hot rock (the system) cools at sunset.
Which of the following would result in work being done by the gas on its surroundings?
A heated gas is allowed to escape into the air. Gas in a piston expands, pushing the piston outward.
A state function is a property that can only be measured if a substance undergoes a phase change. A state function is a quantity of a substance that can be measured without a change in state. A state function is a property that is independent of the path taken to achieve it. A state function depends only on the final state of the system. A state function depends on the initial state of the system.
A state function is a property that is independent of the path taken to achieve it. A state function depends on the initial state of the system.
Which of the following are features of a thermochemical equation? Select all that apply.
All reactants and products are shown with stoichiometric coefficents. Physical states should be shown for each reactant and product. The enthalpy change for the reaction is written after the equation.
Select all the statements that correctly describe how thermochemical equations may be manipulated.
Any exothermic reaction would become an endothermic reaction if its direction were reversed. When an equation is multiplied by a constant, the associated enthalpy change is also multiplied by that constant.
-Q (1/2)Q -2Q 3Q
B = 2A A = (1/2)B 2B = 4A 6A - 3B
A solid initially at 75oC is placed in an insulated water bath initially at 30oC. The temperature of the system reaches 45oC. The change in temperature of the solid was oC, and the change in temperature of the water bath was oC. Be careful with + and - signs!
Blank 1: -30 Blank 2: 15 or +15
-------- is the measurement of heat changes.
Blank 1: Calorimetry
The specific heat (s), is the quantity of required to change the temperature of gram(s) of an object by 1 degree .
Blank 1: heat or energy Blank 2: 1 or one Blank 3: Celsius, C, K, or Kelvin
The total change in the internal energy of a system is the sum of the energy transferred as and/or .
Blank 1: heat, heat exchanged, or heat exchange Blank 2: work or work done
Car engines operate based on the mechanical work done by expanding gases. To calculate the total amount of work done, the of the surroundings is multiplied by the change in the of the gas during expansion. This is known as work.
Blank 1: pressure Blank 2: volume Blank 3: PV or pressure-volume
The study of the heat associated with chemical reactions is called
Blank 1: thermochemistry
Which of the following is the best definition of calorimetry?
Calorimetry is the measurement of heat changes that accompany physical or chemical processes.
Based on the first law of thermodynamics, the energy gained by a system is _____ the energy lost by the surroundings.
Equal To
True or false: To understand the total change that occurs in a state function, we must have a record of the conditions ("states") at all times between the initial and final states.
False
q s m T
Heat Specific heat Mass Temperature
Which of the following options correctly represents the units for specific heat? Multiple choice question. g·°CJg·°CJ gJ⋅°CgJ⋅°C J⋅g°CJ⋅g°C Jg⋅°C
J/g⋅°C
Which of the following values are needed to solve for the specific heat of a heated unknown solid when it is placed in a coffee cup calorimeter? The final temperature of the system The pressure of the system The mass of the water in the cup The mass of the solid The initial temperature of the water The initial temperature of the solid
The final temperature of the system The mass of the water in the cup The mass of the solid The initial temperature of the water The initial temperature of the solid
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 The surroundings near Reaction 1 will become colder as it proceeds. Reaction 2 releases twice as much energy as Reaction 1 absorbs. Reaction 2 will proceed faster than Reaction 1. 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. Reaction 2 is exothermic.
Select all the statements about the study of energy changes that are correct.
Thermochemistry is a branch of thermodynamics. One aspect of thermodynamics is the study of energy transfer in the form of heat.
If the system gains heat as it does work on its surroundings, the total change in internal energy of that system will ______.
be positive, negative, or zero
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
The first law of thermodynamics states that the total amount of --- in the universe remains constant.
energy
In a thermochemical equation, the _____ change is always written next to the balanced chemical equation.
enthalpy
When ΔH for a thermochemical equation is negative, that reaction is _____, while a positive value for ΔH is associated with an _____ reaction.
exothermic; endothermic
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
How is the heat change (q) related to the specific heat (s) when a certain amount of substance (of mass m) undergoes a temperature change (ΔT)? q = smΔTsmΔT q = smΔT q = ΔTsmΔTsm q = smΔT
q = smΔT
qsolid matches Choice ssolid × masssolid × ΔTsolid -qsolid matches Choice qwater ssolid matches Choice − qwatermasssolid×ΔTsolid
qsolid matches Choice ssolid × masssolid × ΔTsolid -qsolid matches Choice qwater ssolid matches Choice − qwatermasssolid×ΔTsolid
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 °C to Tf °C, what is the heat capacity of the entire calorimeter (in kJ/K)? Ti-TfxTi-Tfx xTf-TixTf-Ti xTi-TfxTi-Tf Tf-Tix
xTf-Ti
Which of the following equations correctly defines enthalpy change in terms of internal energy change (U) and gas expansion work (at constant pressure)? ΔH = ΔU + PΔV ΔH = PΔ VΔ UPΔVΔU ΔH = ΔUPΔVΔUPΔV ΔH = U - PV
ΔH = ΔU + PΔV
