Gen Chem CH7: Thermochemistry
How does Enthalpy (∆H) relate to Q?
Enthalpy (∆H) = Q
What equation relates entropy and enthalpy to determine if a reaction is spontaneous or not?
ΔG = ΔH - TΔS ΔG = Change in Gibb's free energy ΔH = Change in enthalpy T = Temperature ΔS = Change in entropy
Write the equation used to determine the enthalpy of reaction. What does it mean if you get +deltaHrxn versus -deltaHrxn?
+deltaHrxn: ENDOTHERMIC -deltaHrxn: EXOTHERMIC
True or false? If a reaction is spontaneous (thermodynamically favorable), then it must occur rapidly.
False. A reaction's kinetics and its thermodynamics are not necessarily related! Thermodynamics only predict if a reaction will be spontaneous, not its rate.
What is the difference between Heat (Q) and Specific Heat (c)?
Heat (Q) is the overall change in heat for a substance. Specific Heat (c) is the degree to which a given substance's temperature will increase based on the amount of heat added. It is the ease with which a substance will heat up.
If a reaction has a negative enthalpy and a negative entropy, what is true about the spontaneity of the reaction at a high temperature? At a low temperature?
If both enthalpy and entropy are negative, then the spontaneity of the reaction will depend on the temperature. If the temperature is high, then it will result in a positive Gibbs free energy and thus a non-spontaneous reaction. If the temperature is low, then it will result in a negative Gibbs free
Compare system and surroundings
System: the matter that is being observed Surroundings: everything outside the system
The area under the curve on a PV diagram is equal to what? What equation does this relate to?
The area under the curve on a PV diagram is equal to work according to the relationship W = P∆V where: W = Work done to/by the gas. P = Pressure ∆V = Change in Volume
What equation can be used to calculate the Enthalpy change for a reaction given Heat of Formation values?
∆H = Hf(products) - Hf(reactants)
In each of the following four types of processes, one variable stays the same in the system. Match each process with its constant parameter. (1) Isobaric (2) Isochoric (3) Isothermal (4) Adiabatic (A) Pressure (B) Temperature (C) Volume (D) Heat
(1) Isobaric (A) Pressure (2) Isochoric (C) Volume (3) Isothermal (B) Temperature (4) Adiabatic (D) Heat [constant at 0, there is no heat transfer at all]
What variables change in the ∆U = Q + W equation for each process? (1) Isobaric (2) Isochoric (3) Isothermal (4) Adiabatic
(1) Isobaric - W changes due to a change in V. (2) Isochoric/metric/volumetric - W does not change due to Volume remaining constant. (3) Isothermal - ∆U remains constant because T remains constant. W and Q also remain constant. (4) Adiabatic - Q does not change. This is the definition of an Adiabatic process. The change of U is caused solely by a change in W
Calculate the heat of formation for the following reaction: 8 Al(s) + 3 Fe3O4(s) → 4 Al2O3(s) + 9 Fe(s) ΔH for Fe3O4(s) = -1120.9 kJ/mol ΔH for Al2O3(s) = -1669.8 kJ/mol (A) -3,316.5 kJ (B) -2,563.6 kJ (C) -1,657.2 kJ (D) -53.9 kJ
(A) -3316.5 kJ For a detailed solution, see problem #1 here: https://www.thoughtco.com/heat-of-formation-example-problem-609556
At what value of delta G is the system in equilibrium? (A) 0 (B) 1 (C) infinity (D) None of the above
(A) 0 when delta G=0 the system is at equilibrium
At what set of conditions do standard enthalpies occur? (A) 25 degrees Celsius and 1.0 atm (B) 100 degrees Celsius and 1.0 atm (C) 25 degrees Celsius and 2.0 atm (D) 25 degrees Celsius and 1.0 mmHg
(A) 25 degrees Celsius and 1.0 atm Standard enthalpy occurs at 25 degrees Celcius and 1.0 atm.
How much Heat is absorbed when 423 grams of Copper (c = .385 J/g⋅C) goes from 22.3°C to 44.4°C (in kJ)? (A) 3.599 (B) 35.99 (C) 359.9 (D) 3599
(A) 3.599 kJ Q = mc∆T Q = (423)(.385J/g⋅C)(22.1°C) Q = approx. 4000 (actual: 3599 J) Remember to convert to kJ!
The 0th Law of Thermodynamics states that if A is in Thermal Equilibrium with B and B is in Thermal Equilibrium with C; therefore, C must be in thermal equilibrium with: (A) A (B) B (C) C (D) D
(A) A The 0th Law of Thermodynamics states that if A is in Thermal Equilibrium with B and B is in Thermal Equilibrium with C; therefore, C must be in thermal equilibrium with A.
The heat of a given reaction is called the change in: (A) Enthalpy (B) Entropy (C) Free energy (D) Temperature
(A) Enthalpy The heat of a given reaction is called the change in enthalpy.
Match the following to the correct description: (A) Isothermal Process (B) Adiabatic Process (C) isobaric Process (D) isovolumetric Process I. no heat is exchanged with the environment so delta Q=W II. Pressure is constant in the system III. occurs at constant volume so deltaU=Q IV. occurs at constant temp and internal energy is constant
(A) Isothermal Process --> IV (B) Adiabatic Process --> I (C) isobaric Process --> II (D) isovolumetric Process --> III
The ΔG value for the formation of gaseous water at 25°C and 1.0 atm is −228 kJ/mol. The formation of gaseous water at these conditions is: (A) Spontaneous (B) Nonspontaneous (C) At equilibrium (D) Not possible
(A) Spontaneous The formation of gaseous water at these conditions is spontaneous because ΔG is negative.
Match the following phase changes to the most accurate description (A) Vaporization (B) Solidification (C) Sublimation (D) Condensation (E) Deposition (F) Fusion I. transition from solid to liquid II. a solid going directly into gas phase III. molecules at surface of liquid have enough kinetic energy to escape to the gas phase IV. transition from gas to solid V. transition from liquid to solid VI. occurs in closed containers where the pressure exerted on the gas forces it back into the liquid state
(A) Vaporization --> III (B) Solidification --> V (C) Sublimation ---> II (D) Condensation --> VI (E) Deposition --> IV (F) Fusion ---> I
The laws of thermodynamics dictate transformations of energy from one form to another. Which law of thermodynamics states that if two systems are in thermal equilibrium with a third system, then the first two systems are also in thermal equilibrium with each other? (A) Zeroth law of thermodynamics (B) First law of thermodynamics (C) Second law of thermodynamics (D) Third law of thermodynamics
(A) Zeroth law of thermodynamics The Zeroth law of thermodynamics highlights the transitive property of thermal equilibrium, and is the basis of the concept of temperature.
Match the following to the correct description: (A) isolated system (B) closed system (C) open system I. system cannot exchange energy or matter with surroundings II. system can exchange energy but not matter with surroundings III. system can exchange both energy and matter with surroundings
(A) isolated system --> I (B) closed system ---> II (C) open system ----> III
Which of the following best describes boiling point? (A) temperature where the VP= ambient pressure (B) temperature where the liquid becomes a gas (C) A and B (D) None of the above
(A) temperature where the VP= ambient pressure
A certain gas performs 45.3 J of work and gains 32.6 J of heat from its surroundings. By how much did its Internal Energy change? (A) -77.9 (B) -12.7 (C) 12.7 (D) 77.9
(B) -12.7 ∆U = Q + W ∆U = 32.6 - 45.3 ∆U = 32.6 - 45.3 ∆U = - 12.7
Consider the following unbalanced reaction: C6H12O6(s) + O2(g) -> CO2(g) + H2O(l) What is the enthalpy change (in kJ) for the combustion of 2 mols of glucose considering the following Heat of Formation values: C6H12O6 = -1260 kJ/mol CO2 = -393.5 kJ/mol H2O = -285.8 kJ/mol (A) -1,292 (B) -5631 (C) 646.2 (D) 5631
(B) -5631 First, balance the reaction as follows: C6H12O6(s) + 6O2(g) -> 6CO2(g) + 6H2O(l) ∆H = Hf(products) - Hf(reactants) ∆H = [6(-393.5)+6(-285.8)] - (-1260) ∆H = approx. -3000 (actual: -2816) for one mole of glucose ∆H = approx. -6000 kJ (actual: -5631)
Given the following equation calculate the delta Hrxn for: C(s,graphite) + 2H2 (g) --> CH4 (g) a) CH4(g) +2O2(g) ---> CO2(g) +2H2O (l) deltaH= -890.4kj/mol b) C(s) +O2(g) ---> CO2(g) deltaH= -393.5 kj/mol c) H2 (g) + 0.5O2(g) ---> H2O (A) 74.7 kj/mol (B) -74.7 kj/mol (C) 85.2 kj/mol (D) -85.2 kj/mol
(B) -74.7 kj/mol To see the work, reference notes from Gen Chem CH7: thermochemistry
Suppose that a reaction has ΔH= -77 kJ and ΔS= -0.48 kJ. At what temperature will it change from spontaneous to non-spontaneous? (A) 47 K (B) 160 K (C) 243 K (D) 321 K
(B) 160 K ΔG = ΔH - TΔS 0 = (-77) - T(-0.48) 77 = 0.48T T = about 150K (actual 160.4K)
Calculate Gibb's free energy for a reaction in which the overall change in entropy is -24.3 kJ and the overall change in enthalpy is -2354.98 kJ (at a Temperature of 25°C)? (A) 9,596.38 (B) 4,886.42 (C) -4,886.42 (D) -9,596.38
(B) 4,886.42 ΔG = ΔH - TΔS ΔG = -2354.98 - (298K ⋅ -24.3 kJ) ΔG = -2354.98 - (approx. -7500 kJ (actual: -7,241.4)) ΔG = approx. 5,000 (actual: 4,886.42)
One cup containing 100g of H2O at 300K is mixed into another cup containing 200g of H2O at 450K. What is the equilibrium temperature of the system? (A) 300K (B) 400K (C) 440K (D) 510K
(B) 400K qcold = -qhot (100g) (1cal/gK) (Tf-300) = -[200*1*(Tf-450)] 100Tf-30,000 =90000-200Tf 300Tf=120000 Tf=400K
You have 4.3 kg of water (c = 4186 J/kg⋅C; L = 2260 J/kg). How much Heat would it take to convert all of the water into vapor if the current temperature of the water is 53.7°C? (A) 1,423 (B) 843,109 (C) 1,423,675 (D) 2,143,896
(B) 843,109 Qtotal = Qheat + Qphase Qtotal = mc∆T + mL Qtotal = (4.3)(4186)(100-53.7) + (4.3)(2260) Qtotal = (approx. 800,000 (actual: 833,390.74)) + (approx. 9,000 (actual: 9,718)) Qtotal = (approx. 809,000 (actual: 843,108.74))
In which of the following types of systems would any thermodynamic process have to either increase entropy or keep entropy the same? (A) Open System (B) Closed System (C) Both A and B (D) Neither A nor B
(B) Closed System In a Closed system, any thermodynamic process must keep entropy the same or increase it.
If the ΔH of a reaction is negative, the reaction is: (A) Endothermic (B) Exothermic (C) In equilibrium (D) Endergonic
(B) Exothermic If the ΔH of a reaction is negative, the reaction is exothermic.
When 1.0 mole of ZnO(s) decomposes, the ΔH = 348 kJ/mol of heat energy. This tells you that the formation of ZnO(s) is: (A) Endothermic (B) Exothermic (C) In equilibrium (D) Endergonic
(B) Exothermic The FORMATION of ZnO(s) is exothermic because it is the reverse reaction of the decomposing.
The laws of thermodynamics dictate transformations of energy from one form to another. Which law of thermodynamics states that the total amount of energy in the universe is constant? (A) Zeroth law of thermodynamics (B) First law of thermodynamics (C) Second law of thermodynamics (D) Third law of thermodynamics
(B) First law of thermodynamics The first law of thermodynamics states that the total amount of energy in the universe is constant.
Within a system, which of the following are possible? I. Energy increases without the Surroundings changing II. Energy is Destroyed III. Energy is transformed from one form to another (A) I only (B) III only (C) I and III only (D) I, II and III
(B) III only According to the Law of Conservation of Energy, Energy cannot be Created (I) nor Destroyed (II), only transformed from one form to another.
Which of the following best represents the equation used to determine the change in entropy of a system? (A) S= T/Q (B) S= Q/T (C) S= T/G (D) S= G/T
(B) S= Q/T the change in entropy is determined by dividing the amount of heat gained/lost by the temperature UNITS: J/mol*K
Hess's Law is true for variables such as enthalpy and entropy because these are _________ variables. (A) Process (B) State (C) Fixed (D) Variable
(B) State Hess's Law is true for variables such as enthalpy and entropy because these are state variables.
At a constant pressure, the change in enthalpy is equal to what? (A) The temperature change (B) The heat added to the system (C) The molarity change (D) The disorder added to the system
(B) The heat added to the system At a constant pressure, the change in enthalpy is equal to the heat added to the system.
What equation is used to determine the amount of heat needed for a phase change? (A) q=mcdeltaT (B) q=mL (C) q= deltaU - W
(B) q=mL during phase changes the the values used are based on enthalpy you cannot used the q=mcdeltaT because the temperature is constant (delta T =0)
The formation of Nitrogen dioxide is a two step process: N2 + O2 -> 2NO ΔH = 170 kJ 2NO + O2 -> 2(NO2) Δ H = -122 kJ What is the change in enthalpy when creating 4 moles of nitrogen dioxide? (A) 48 kJ/mol (B) -48 kJ/mol (C) 96 kJ/mol (D) -96 kJ/mol
(C) 96 kJ/mol Hess's Law states that a change in enthalpy for a total reaction can be calculated by summing the enthalpy changes for every step involved in the reaction: 170 + (-122) = 48 kJ 48 kJ is the total change in enthalpy for the reactions that produce only 2 moles of Nitrogen dioxide. Since the question asks for 4 moles of Nitrogen dioxide, the enthalpy must be doubled. (48 kJ/ 2 mol NO2)* 2 = 96 kJ/ 4 mol NO2 Thus the answer is 96 kJ
Which of the following can Entropy measure? (A) How much energy is spread out. (B) How widely energy spreads out during some process (C) Both A and B (D) Neither A nor B
(C) Both A and B Entropy can measure each of the following: (A) How much energy is spread out. (B) How widely energy spreads out during some process
Fill in the blanks: If ____________ is increasing the thermal energy in the system, then the temperature of that system is _______________. (A) Kinetic Energy, Increasing (B) Kinetic Energy, Decreasing (C) Heat, Increasing (D) Heat, Decreasing
(C) Heat, Increasing If Heat is increasing the thermal energy in the system, then the temperature of that system is Increasing.
The process of dissolving Na2SO4 in water is known to be exothermic: Na2SO4(s) = 2 Na + (aq) + SO42 - (aq) + heat If the temperature of the solution is decreased, Na2SO4 becomes: (A) Less soluble (B) No change in solubility occurs (C) More soluble (D) None of the above
(C) More soluble If the temperature of the solution is decreased, Na2SO4 becomes more soluble. This is because heat is being taken away which shifts the reaction to the right. However, to shift the reaction to the right, Na2SO4 (s) must be more soluble.
The laws of thermodynamics dictate transformations of energy from one form to another. Which law of thermodynamics states that systems will always favor an increase in entropy? (A) Zeroth law of thermodynamics (B) First law of thermodynamics (C) Second law of thermodynamics (D) Third law of thermodynamics
(C) Second law of thermodynamics The second law of thermodynamics states that systems will always favor an increase in entropy.
Fill in the blanks: At very low pressures and temperatures, a solid may transition to a gas in a process called _______________; the reverse process is called ______________. (A) Melting, Freezing (B) Vaporizing, Condensing (C) Sublimation, Deposition (D) Supercritical Evaporation, Supercritical Freezing
(C) Sublimation, Deposition At very low pressures and temperatures, a solid may transition to a gas in a process called Sublimation; the reverse process is called Deposition.
when is entropy maximized? (A) when Q> Keq (B) when Q< Keq (C) at equilibrium
(C) at equilibrium entropy is maximized at equilibrium
What equation would you use to determine the free energy of a reaction at equilibrium? (A) delta G= delta H - T(deltaS) (B) delta G = (sum of free energy of products) - (sum of free energy in reactants) (C) delta G= -RTln(Keq) (D) delta G= delta G (knot) + RTlnQ
(C) delta G= -RTln(Keq)
Which of the following best describes vapor pressure? (A) pressure a gas exerts over a solid at equilibrium (B) pressure the liquid exerts on the gas at equilibrium (C) pressure the gas exerts over a liquid at equilibrium (D) pressure the solid exerts over a gas at equilibrium
(C) pressure the gas exerts over a liquid at equilibrium
What is the change in enthalpy for the following reaction: 2Mg + O2 -> 2MgO, if ΔH Mg = 0 kJ, ΔH O2 = 0 kJ, and ΔH MgO = -501 kJ? (A) 1,002 kJ/mol (B) 501 kJ/mol (C) -501 kJ/mol (D) -1,002 kJ/mol
(D) -1,002 kJ/mol The change in enthalpy is: (ΔH products) - (ΔH reactants) Thus the answer is -1,002 kJ/mol.
Calculate the deltaHrxn of C(s) + 2H2 (g) ---> CH4(g) given that: deltaH of formation (C) = 715 kJ/mol deltaH (H-H) = 436 kJ/mol and deltaH (C-H)= 415kJ/mol (A) 57 kJ/mol (B) -57 kJ/mol (C) 73 kJ/mol (D) -73 kJ/mol
(D) -73 kJ/mol To see the work, reference notes from Gen Chem CH7: thermochemistry
Which of the following processes would NOT result in a positive ΔS? (A) Sublimation (B) Evaporation (C) Melting (D) Freezing
(D) Freezing An increase in ΔS would signify more microstates (or randomness) are possible, based on the definition of entropy. Only freezing will decrease the randomness of the arrangement of molecules of the previous choices.
Equilibrium is a state of dynamic molecular behavior, meaning that: (A) Reactants continually turn into products at a progressively slower rate (B) Products continually turn into reactants at a progressively faster rate (C) Reactants turn into products and products turn into reactants at different rates (D) Reactants turn into products and products turn into reactants at equal rates
(D) Reactants turn into products and products turn into reactants at equal rates Equilibrium is a state of dynamic molecular behavior, meaning that reactants turn into products and products turn into reactants at equal rates.
The laws of thermodynamics dictate transformations of energy from one form to another. Which law of thermodynamics states that the entropy of a system approaches some constant value as its temperature approaches absolute zero? (A) Zeroth law of thermodynamics (B) First law of thermodynamics (C) Second law of thermodynamics (D) Third law of thermodynamics
(D) Third law of thermodynamics The third law of thermodynamics states that the entropy of a system approaches some constant value as its temperature approaches absolute zero.
What equation would you use to determine the free energy of a reaction in progress? (A) delta G= delta H - T(deltaS) (B) delta G = (sum of free energy of products) - (sum of free energy in reactants) (C) delta G= -RTln(Keq) (D) delta G= delta G (knot) + RTlnQ
(D) delta G= delta G (knot) + RTlnQ this equation is also equal to RTln(Q/Keq)
How would delta G be affected if (Q/Keq) > 1 and if (Q/Keq) < 1?
(Q/Keq) > 1 ---> reaction is NON-SPONTANEOUS (Q/Keq) < 1 ---> reaction is SPONTANEOUS
What does a -delta G and +delta G represent?
-delta G: reaction is SPONTANEOUS +delta G: reaction is NONSPONTANEOUS
Above the Critical Point, the molecules are considered a Supercritical Fluid. What is that?
A Supercritical Fluid is a fluid with both liquid- and gas-like properties.
Recall that Systems are a portion of the universe (an object or some group of objects) we could observe. Which of the following types of Systems cannot exchange energy or matter with its surroundings? (A) Isolated System (B) Closed System (C) Open System (D) Both A and B
A) Isolated System An Isolated System is not capable of exchanging energy or matter with their systems.
Compare Open and Closed Systems in terms of what they are capable of exchanging with their surroundings.
An Open system is able to exchange both energy and matter with its surroundings. A Closed system is only able to exchange energy, but not matter, with its surroundings.
As the Internal Energy of a gas increases, what happens to the temperature of the gas?
As the Internal Energy of a gas increases, the temperature of the gas also increases.
Compare constant pressure and Constant volume calorimetry give an example of each?
Constant pressure: (coffee cup calorimetry) pressure remains constant and temperature is measure as the reaction progresses Constant Volume: (bomb calorimetry) volume is constant so no work is being done (W=pdeltaV) also no heat exchange is occurring between the calorimeter and environment therefore qsystem= -qsurroundings
Compare Enthalpy of Fusion and Enthalpy of Vaporization
Enthalpy of Fusion: used when transitioning from the solid to liquid phase Enthalpy of Vaporization: used at the liquid/gas boundary
What is the difference between exothermic reactions and endothermic reactions in terms of enthalpy?
Exothermic reactions have a ΔH < 0, which means that the reaction is releasing heat. Endothermic reactions have a ΔH > 0, which means that the reaction is absorbing heat.
T/F Free energy tells us whether or not a reaction is exothermic/endothermic while enthalpy tells us about the reactions spontaneity
F Free energy tells us whether the reaction is spontaneous/nonspontaneous Enthalpy tells us if the reaction is endothermic/exothermic
T/F State functions are dependent of the path (process) taken but they are independent of each other
F State Functions are INDEPENDENT of the path taken but are DEPENDENT of each other
T/F the rate of reaction is dependent on delta G no activation energy
F the rate of reaction is dependent on ACTIVATION ENERGY
T/F the standard heat of formation of an element in their standard state is equal to 1
F the standard heat of formation of an element in their standard state is equal to ZERO (0)
True or false? A change in entropy for a reaction that is greater than 0 implies that the reaction went from a less ordered state to a more ordered state.
False. A change in entropy for a reaction that is greater than 0 implies that the reaction went from a more ordered state to a less ordered state. Entropy is a measure of DISorder.
True or false? Knowing that Work is the integral of the PV curve, Isobaric processes do no work.
False. Knowing that Work is the integral of the PV curve, Isochoric processes do no work. This is because there is no change in the volume (x), so there is no area under the curve (really a vertical line).
Fill in the blanks: Fusion occurs at the _____ point while solidification occurs at the _____ point
Fusion occurs at the MELTING point while solidification occurs at the FREEZING point
What is the thermodynamic quantity that combines enthalpy and entropy? What is its units?
Gibbs free energy (ΔG) is the thermodynamic quantity that combines enthalpy and entropy. Its units are J/mol.
Why is Gibbs free energy being a state function important in calculating ΔG and if a series of reactions is favorable?
Gibbs free energy being a state function means that ΔG values for different reactions can be added together to see if the overall reaction is favorable or not. It allows for coupling of reactions.
Compare Heat (Q) and Temperature (T) in terms of thermal energy.
Heat is the Transfer of thermal energy between a system and its environment, whereas Temperature is the macroscopic features of having different thermal energy levels (i.e. a high temperature feeling "hot" and having high thermal energy).
What is the difference between heat, temperature, and enthalpy?
Heat is the transfer of energy due to change in temperature. Temperature is the measure of the average kinetic energy of molecules. Enthalpy is referred to as the heat transfer from the perspective of the system during reactions.
If a reaction has a positive enthalpy and a positive entropy, what is true about the spontaneity of the reaction at a high temperature? At a low temperature?
If both enthalpy and entropy are positive, then the spontaneity of the reaction depends on the temperature. If temperature is high, then it will result in a negative Gibbs free energy and thus a spontaneous reaction. If the temperature is low, then it will result in a positive Gibbs free energy and thus a non-spontaneous reaction.
Which of the following would increase the energy in the system? Which would increase the energy in the surroundings? - Work done on a system - Work done by a system - Heat into a system - Heat out of a system
Increasing the energy of the system: - Work done on a system - Heat into a system Increasing the energy of the surroundings: - Work done by a system - Heat out of a system
Name the variables involved in state functions
Pressure, density, temperature, volume, enthalpy, internal energy, free energy, entropy **When I'm under PRESSURE and feeling DENSE all I want to do is watch TV and get HUGS**
What equation allows you to determine the amount of energy required to cause a phase change in a certain amount of a substance?
Q = mL Q = Heat m = Mass L = Latent Heat of Fusion (or Vaporization)
What equation can be used to relate heat (Q) and Specific Heat (c)?
Q = mc∆T Q = Heat m = Mass c = Specific Heat ∆T = Change in Temperature (in C or K)
For the following reaction, how will the reaction equilibrium be affected by an increase in temperature? H2O2(l) -> H2(g) + O2(g), delta H = 187 kJ
Since delta H is a positive value it indicates that it is an endothermic reaction and the energy is on the reactant side because it is being absorbed. Thus an increase in the temperature of the system causes equilibrium to shift towards the right, towards the products H2(g) and O2(g) because this causes the reaction to shift away from the heat to balance out the reaction.
Compare standard conditions and STP. When would you use each?
Standard Conditions: 25 degrees celsius (298K), 1 atm, 1M concentrations used for kinetics, thermodynamics, and equilibrium STP: 0 degrees celsius, 1 atm used for ideal gas calculations
Compare state functions and process functions
State functions: describes the physical properties of an equilibrium state Process Function: defines the path between equilibrium
T/F heat is transferred from the warm substance to the cold substance
T
T/F standard heat of formation is the the enthalpy required to produce 1 mole of a compound from its elements in their standard state
T
T/F gibbs free energy is temperature independent
T Free energy is TEMPERATURE DEPENDENT
T/F one can used bond dissociation energies to determine the the enthalpy of a reaction
T bond dissociation energies can be use to calculate the enthalpy. It does so by summing the enthalpy of the broken bond and subtracting that value by the sum of enthalpy os bonds formed
T/F entropy in the universe is always increasing
T this is a restatement of the second law of thermodynamics. The entropy in the universe is always increasing
True or false? It is better to think of Entropy as energy spontaneously spreading out when possible, rather than things being disordered.
T It is better to think of Entropy as energy spontaneously spreading out when possible, rather than things being disordered.
What's the difference between Temperature and Heat?
Temperature: the average kinetic energy of the particles of a substance; also a state function Heat: the transfer of energy from one substance to another due to their differences in temperature; also a process function
When talking about Thermodynamics, it is important to clarify what the System is and what the Surroundings/Environment are. Compare the two.
The System is the group of objects (or single object) that you are considering, whereas the Surroundings/Environment are all of the objects and forces outside of the system.
The change in enthalpy is the change in heat energy of a reaction. How is enthalpy calculated for a given reaction?
The change in enthalpy is essentially calculated by: (sum of heat content of products) - (sum of heat content of reactants).
Would the formation of the product be favored or not if the ΔG value is positive?
The formation of the product would not be favored if delta G is positive. A positive ΔG means the reaction would require huge amounts of energy to form the product.
If a reaction has a positive value for its enthalpy and a negative value for its entropy, what is true about the spontaneity of the reaction at a high temperature? At a low temperature?
The reaction is always non-spontaneous because it will result in a positive Gibbs free energy value (delta G).
The reaction is always non-spontaneous because it will result in a positive Gibbs free energy value (delta G).
The reaction is always spontaneous because it will result in a negative Gibbs free energy value (-ΔG).
When more reactant is added into a reaction system at equilibrium, how does the system react to compensate for the stress that is applied according to Le Chatlier's principle?
The system reacts by favoring the shift towards the products to make more product in order to relieve the stress from the extra added reactants.
If the reaction quotient (Q) is greater than the equilibrium constant (K), what is true about the the value of Gibbs free energy?
The value of Gibbs free energy is greater than zero (or is a positive number) because if the reaction quotient (Q) is greater than the equilibrium constant (K), then the reaction has exceeded the equilibrium state.
Compare the critical point and triple point in a phase diagram
Triple point: where all 3 phases exist in EQUILIBRIUM Critical Point: at temperatures and pressure above this point, the liquid and gas phase are INDISTINGUISHABLE
True or false? A reaction can be both exergonic and endothermic.
True. A reaction can be both exergonic (spontaneous) and endothermic (requiring heat). However, these reactions are quite rare, and must have a high increase in entropy. A common example would be an instant icepack!
True or false? All spontaneous reactions are irreversible.
True. All spontaneous reactions are irreversible.
True or false? Although the universe is a closed system, it is always expanding, so entropy can continue to increase.
True. Although the universe is a closed system, it is always expanding, so entropy can continue to increase.
True or false? Hess's Law states that the energy change of a process is independent of the path that was taken to get there.
True. Hess's Law states that the energy change of a process is independent of the path that was taken to get there.
True or false? If a reaction is reversed, then the sign of ΔH is also reversed.
True. If a reaction is reversed, then the sign of ΔH is also reversed.
True or false? The specific heat of a substance depends upon the phase the substance is in.
True. The specific heat of a substance depends upon the phase the substance is in.
Why can't the equation q=mcdeltaT be used for determining the amount of heat needed for a phase change?
because at the phase change temperature is constant therefore delta T=0 this doesn't make any sense so the heat is determined through the use of enthalpy using the equation q=mL where L =latent heat (enthalpy of fusion or vaporization) and m=mass
What is the specific heat of water in calories?
c= 1 cal/gK
Why does deltaH = Q at constant pressure?
delta H = Q+W W=pdeltaV if P is constant that means its equal to zero W=0 DeltaH =Q
What does it mean when delta Q> 0? How about when deltaQ<0?
deltaQ> 0 --> endothermic --> system absorbs energy deltaQ<0 --> exothermic --> system releases energy
What is the first law of thermo equation that related heat and work?
deltaU= Q-W
IS the entropy of the universe greater or less than zero? Why?
the entropy of the universe is greater or equal to zero. This is because the second law of thermodynamics states that entropy in the universe is always increasing
What is Hess's Law?
the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process
What is the standard state of an element?
the standard state is the most prevalent form of the element under standard conditions
What is another method of thinking about entropy instead of disorder?
thinking of entropy as how dispersed energy is
How can non-spontaneous reactions be given the energy it needs to go forward?
use reaction coupling to couple spontaneous and nonspontaneous reactions together
Draw a heating curve and explain what is happening in the rising phase and constant phase
when a compound is heated --> temperature rises until MP is reached --> Temperature remains constant until the entire compound has converted from solid to liquid --> after all has been converted the temperature rises again to the BP --> Temperature will again remain constant until all of the liquid has been converted into gas --> then temp can rise again
If the reaction is endothermic, what is the sign of ΔH?
ΔH is positive for an endothermic reaction.
