Thermodynamics
What is the final temperature of a 3 kg wrought iron fireplace tool that is left in front of an electric heater, absorbing heat energy at a rate of 100 W for 10 minutes? Assume the pendant is initially at 20 °C and that the specific heat of wrought iron is 500 J/kg*K. A. 40 °C B. 50 °C C. 60 °C D. 70 °C
C. 60 °C Watts are equal to J/s E = P * t = 100W * 10 min (60 s / 1 min) = 60000 J q = mcΔT 60000 = 3 500 ΔT 40 °C = ΔT BUT ADD ORIGINAL TEMP 20 + 40 = 60 °C
Which of the following scenarios violates the first law of thermodynamics, "the conservation of energy?" A. An efficient wind turbine that converts all of its energy from mechanical movement into electrical potential energy. B. A machine that converts heat energy into work energy. C. A spring that extends and retracts forever, alternating between potential and kinetic energy. D. An isolated electrochemical cell that indefinitely generates an electrical current.
D. An isolated electrochemical cell that indefinitely generates an electrical current.
vaporization
Liquid to gas (boiling; evaporation)
heat of vaporization
The amount of energy required for the liquid at its boiling point to become a gas
latent heat
heat absorbed or radiated during a change of phase at a constant temperature and pressure
solidification
liquid to solid (freezing)
If ∆S is = 0, is the process spontaneous or not spontaneous?
neither, it is at equilibrium
adiabatic
no heat exchange Q = 0
isolated systems
not capable of exchanging energy or matter with their surrounding; as a result, the total change in internal energy must be zero
If ∆S is < 0, is the process spontaneous or not spontaneous?
not spontaneous
if heat flows into the system, then Q will be positive or negative?
positive
Gibb's free energy
predictor of spontaneity of a chemical reaction
sublimation
solid to gas
isochoric PV diagram
straight vertical line no work because there is no area
internal energy
the sum of the kinetic and potential energies of all particles in the system
second law of thermodynamics
the total change in entropy of a system plus its surroundings will always increase for a spontaneous process
state functions
thermodynamics properties that are a function of only the current equilibrium state of a system; defined by the fact that they are independent of the path taken to get to a particular equilibrium state
equation for thermal expansion
ΔL= αLΔT ΔL: change in length α: coefficient of linear expansion L: original length ΔT: change in temp
formula for volumetric thermal expansion
ΔV = βVΔT ΔV: change in volume β: coefficient of volumetric expansion V: original volume ΔT: change in temp
60 J of work is done on a gas, and the gas loses 150 J of heat to its surroundings. What is the change in internal energy?
-90 J ∆U = Q + W ∆U = -150 + 60 = -90 J
isothermal PV diagram
1/x function because PV = nRT P = nRT/V nRT are all constants so P = 1/V area under "curve" is work done by the gas
A 20 m steel rod at 10 °C is dangling from the edge of a building and is 2. cm from the ground. If the rod is heated to 110 °C, will the rod touch the ground? (Note: α = 1.1⁻⁵ x 10 K⁻¹) A. Yes, because it expands by 3.2 cm B. Yes, because it expands by 2.6 cm C. No, because it expands by 2.2 cm D. No, because it expands by 1.8 cm
C. No, because it expands by 2.2 cm ΔL = αLΔT ΔL = 1.1⁻⁵ * 20 m * 100 K = 0.022 m = 2.2 cm
When heating a solution, a scientist detects a temperature increase in the solution during a period of time. Which of the following statements accurately characterizes the solution during this period? A. The solution's temperature increase is proportional to its ΔH(vaporization) B. The solution is undergoing a phase change. C. The velocity of molecules in the solution is increasing. D. The solution is at boiling point.
C. The velocity of molecules in the solution is increasing.
open system
a system that freely exchanges both energy and matter with its surroundings
if work is done on the system, then W will be positive or negative?
positive
isobaric PV diagram
straight horizontal line area under "curve" is work done by the gas
third law of thermodynamics
the entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero
equation for Gibb's free energy change
∆G = ∆H - T∆S
A gas starts with 200 J of internal energy. While you add 180 J of heat to the gas, the gas does 70 J of work. What is the final energy of the gas?
310 J ∆U = Q + W ∆U = +180 - 70 ∆U = 110 J 200 + 110 = 310 J
1 cal = ? J
4.184 J
specific heat of water
4.184 J/g*K OR 1 cal/g*K
A hot object is placed next to a cold object so that they are touching. Which of the following statements is true? I. Heat will transfer from the hot object to the cold object because the hot object has a higher temperature. II. The two objects are in thermal equilibrium III. Internal energy will transfer from the hot object to the cold object because the hot object has greater internal energy. A. I only B. II only C. I and III D. III
A. I only
A certain substance has a specific heat of 1 J/mol * K and a melting point of 350 K. If one mole of the substance is currently at a temperature of 349 K, how much energy must be added in order to melt it? A. More than 1 J B. Exactly 1 J C. Less than 1 J but more than 0 J D. Less than 0 J
A. More than 1 J After the substance reaches its melting point, additional heat is needed to actually induce the phase change
The entropy of a system can: A. never decrease B. decrease when the entropy of the surroundings increases by at least as much C. decrease when the system is isolated and the process is irreversible D. decrease during an adiabatic reversible process
B. decrease when the entropy of the surroundings increases by at least as much
Additional gas is pumped inside a rigid container that stores compressed gas. Which of the following is a true statement about this system? A. Pressure is constant throughout the compression. B. The volume of the container is decreasing. C. There is no work done on the container. D. The molar concentration of gas is decreasing.
C. There is no work done on the container. A rigid container does not change in volume, it is an isochoric system. There is no work done in an isochoric system
if heat flows out of the system, then Q will be positive or negative?
negative
thermal equilibrium
when two systems are in contact with each other and no energy flow takes place between them, then the two systems are said to be in thermal equilibrium with each other
What is the heat energy required to completely vaporize 10 g of water beginning at 0 °C? (The heat capacity of water is 4.2 J/g⋅K and the ΔH(vaporization) of water is 2260 kJ/kg). A. 4.9 kJ B. 26.8 kJ C. 228.1 kJ D. 2126 kJ
B. 26.8 kJ q=mCΔT ΔT = 100 - 0 = 100 q = 10 * 4.2 * 100 = 4200 J Once the water has reached its boiling point it requires heat to vaporize into gas. This is equal to 2260 kJ in our case with 10 g of water 4.2 + 22.6 = 26.8
While 40 J of work are done on a gas, the internal energy goes down by 150 J. What was the value of the heat added to the gas?
Q = -190 J -150 J = Q + 40 J Q = -190 J
In an exothermic process, the volume of a gas expanded from 186 mL to 1997 mL against a constant pressure of 745 torr. During the process, 18.6 calories of heat energy were given off. What was the internal energy change for the system in joules? Also, (1 L atm = 101.3 J)
-257.12 J Q = heat given off by system = 18.6 cal = 18.6 x 4.184 J (remember: 1 cal = 4.184 J) = 77.82 J Since heat flows out of the system, Q will be negative. So Q = -77.82 J 760 torr = 1 atm, so 745 torr of pressure = 745/ 760 = 0.98 atm Volume should be in litres (L), thus ∆V = (1997 - 186) ml = 1811 mL = 1811 X 10⁻³ L W = P∆V W = 0.98 * 1.811 = 1.77 atm*L 1.77 atm*L x 101.3 = 179.30 J In this example, work is being done by the system in expansion of the gas, so W is negative (remember: if work is done by the system, then W will be negative). Therefore, W = -179.30 J So, net change in internal energy of the system (∆U) = Q + W = -77.82 + (-179.30) = -257.12 J
How much heat is required to completely melt 500 g gold earrings, given that their initial temperature is 25 °C? (The melting point of gold is 1064 °C, its heat of fusion is 6.37 x 10⁴ J/kg, and its specific heat is 126 J/kg*K). A. 15 kJ B. 32 kJ C. 66 kJ D. 97 kJ
D. 97 kJ 1st: Determine how much heat is required to raise the temp of the earrings to the melting point of gold. q = mcΔT = 0.5 kg (126)(1039K) = 60 kJ 2nd: Calculate the heat required to actually melt the earrings (the latent heat) q = mL = 0.5kg (6.37 x 10⁴) = 32 kJ 3rd: Add the two energies together to determine the total heat required q = 60 kJ + 32 kJ = 92 kJ, similar to choice D
condensation
Gas to liquid
closed system
a system that exchanges only energy with its surroundings, not matter
isobaric
constant pressure
isothermal
constant temperature ∆T = 0 ∆U = 0
isochoric
constant volume also isometric or isovolumetric
process functions
describe path taken to get from one state to another; ex: work and heat
deposition
gas to solid
heat always flow from _________ temperature to _____________ temperature
high; low
Zeroth Law of Thermodynamics
if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with one another
first law of thermodynamics
law of conservation of energy; energy can neither be created nor destroyed; it can just be converted from one form to another. the change in internal energy of a closed system is equal to the energy added to it in the form of heat (Q) plus the work (W) done on the system by the surroundings. ∆E (internal) = Q+W
if work is done by the system, then W will be positive or negative?
negative
equation for heat transfer during phase change
q = mL q: amount of heat gained or lost from the material m: mass of the substance L: heat of transformation (latent heat) of the substance there is no temp change in a phase change, so no need for ΔT in equation
equation for heat transfer
q = mcΔT m: mass c: specific heat of the substance ΔT: change in temp (C or K)
adiabatic PV diagram
similar to isothermal, but steeper
fusion
solid to liquid (melting)
If ∆S is > 0, is the process spontaneous or not spontaneous?
spontaneous
Which of the following is NOT a state function? A. internal energy B. heat C. temperature D. entropy
B. heat
heat of fusion
Amount of energy required to change a substance from the solid phase to the liquid phase.
The work done when a gas is compressed in a cylinder is 820 J. At the same time, the system lost 320 J of heat to the surrounding. What is the energy change of this system?
500 J Here the gas is the system. First you must decide the signs of 'W' and 'Q' using the convention discussed earlier. Work is done on the system, so W = + 820 J and heat is lost by the system, so Q = - 320 J. ∆E = Q + W = - 320 J + 820 J = 500 J
Equal amounts of heat are absorbed by 100 g samples of various solid metals with differing specific heat values. Which of the following statements is true regarding metals and their specific heat values? A. The metal with the greatest specific heat will undergo the smallest change in temperature. B. The metal with the smallest specific heat will undergo the smallest change in temperature. C. The metal with the greatest specific heat will resist melting to a greater degree at its melting point. D. The metal with the smallest specific heat will resist melting to a greater degree at its melting point.
A. The metal with the greatest specific heat will undergo the smallest change in temperature.
In a system undergoing adiabatic compression, what are the values of internal energy and heat if work done on the system is 500 J? A. internal energy is 500 J and heat is 0 J B. internal energy is 0 J and heat is -500 J C. internal energy is 0 J and heat is 500 J D. internal energy is -500 J and heat is 0 J
A. internal energy is 500 J and heat is 0 J ∆U = Q + W adiabatic means that Q = 0, so B and C are wrong ∆U = W 500 = 500
In an adiabatic compression process, the internal energy of the gas: A. increases because the work done on the gas is negative B. increases because the work done on the gas is positive C. decreases because the work done on the gas is negative D. decreases because the work done on the gas is positive
B. increases because the work done on the gas is positive Adiabatic process means that there is no exchange of heat (Q = 0) When a gas is compressed, positive work is being done on the gas (rather than by the gas), so the value for work done by the gas will be negative (W < 0) So, if ΔU = Q - W and Q is zero and W is negative, then ΔU is positive
In experiment A, a student mixes ink with water and notices that the two liquids mix evenly. In experiment B, the student mixes oil with water; in this case, the liquids separate into two different layers. The entropy change is: A. positive in experiment A and negative in experiment B B. positive in experiment A and zero in experiment B C. negative in experiment A and positive in experiment B D. zero in experiment A and negative in experiment B
B. positive in experiment A and zero in experiment B When the ink randomly intersperses throughout the water, the final stat is more disordered than the initial state, so the entropy change of the system is positive When the oil separated from the water, the final state is just as ordered as the initial state, so the entropy change in zero
If an object with an initial temperature of 300 K increases its temperature by 1 °C every minute, by how many degrees Fahrenheit will its temperature have increased in 10 min? A. 6 °F B. 10 °F C. 18 °F D. 30 °F
C. 18 °F a change of 1 °C = a change of 1.8 °F
Which of the following processes is LEAST likely to be accompanied by a change in temperature? A. The kinetic energy of a gas is increases through a chemical reaction B. Energy is transferred to a solid via electromagnetic waves. C. A boiling liquid is heated on a hot plate D. A warm gas is mixed with a cold gas
C. A boiling liquid is heated on a hot plate
Atmospheric gases absorb more energy than they emit. If we consider a gas to be a closed system, which of the following is true? A. The change in volume of the gas is negative. B. The work done on the gas is equal to the change in internal energy and the heat absorbed by the gas. C. The heat absorbed by the gas is positive. D. The internal energy of the gas increases.
C. The heat absorbed by the gas is positive. When there is heat entering into the system, Q is positive.
There is a thick metal container with two compartments. One compartments is full of a hot gas, while the other is full of a cold gas. What is the primary mode of heat transfer in this system? A. radiation B. convection C. conduction D. enthalpy
C. conduction The gas only has contact with the metal compartment, so it is not convection, but conduction.
Substances A and B have the same freezing and boiling points. If solid samples of both substances are heated in the exact same way, substance A boils before substance B. Which of the following would NOT explain this phenomenon? A Substance B has a higher specific heat B. substance B has a higher heat of vaporization C. substance B has a higher heat of fusion D. substance B has a higher internal energy
D. substance B has a higher internal energy The heat required to bring the liquid to its boiling point is determined by the specific heat, so A is incorrect The heat required to boil the liquid is determined by the heat of vaporization, so B is incorrect The heat required to melt the solid is determined by heat of fusion, so C is incorrect
