Podcast
Questions and Answers
What is the mathematical expression for enthalpy?
What is the mathematical expression for enthalpy?
- H = E - PV
- H = P + V + E
- H = E + PV (correct)
- H = PV + E
What does a positive value of ΔH indicate about a process?
What does a positive value of ΔH indicate about a process?
- The system is at thermal equilibrium.
- The system is losing energy.
- The process is exothermic.
- The process absorbs heat. (correct)
What is a characteristic of a spontaneous change in a thermodynamic system?
What is a characteristic of a spontaneous change in a thermodynamic system?
- It results in no change in enthalpy.
- It occurs without any energy transfer.
- It is accompanied by an increase in internal energy.
- It is accompanied by a decrease in internal energy or enthalpy. (correct)
According to the Zeroth Law of Thermodynamics, what is true if two systems are in thermal equilibrium with a third system?
According to the Zeroth Law of Thermodynamics, what is true if two systems are in thermal equilibrium with a third system?
In the context of the First Law of Thermodynamics, what does ΔE equal?
In the context of the First Law of Thermodynamics, what does ΔE equal?
What defines a system in thermal equilibrium?
What defines a system in thermal equilibrium?
What occurs when ΔH is negative?
What occurs when ΔH is negative?
Which of the following statements is correct regarding thermodynamic equilibrium?
Which of the following statements is correct regarding thermodynamic equilibrium?
During a reversible expansion of gas, what happens to external pressure?
During a reversible expansion of gas, what happens to external pressure?
What is the unit for measuring enthalpy change?
What is the unit for measuring enthalpy change?
What does the First Law of Thermodynamics entail about energy in an isolated system?
What does the First Law of Thermodynamics entail about energy in an isolated system?
What does the change in enthalpy (ΔH) equal when the pressure is constant during a reaction?
What does the change in enthalpy (ΔH) equal when the pressure is constant during a reaction?
If two objects are in thermal equilibrium, what can be said about their temperatures?
If two objects are in thermal equilibrium, what can be said about their temperatures?
What is the correct expression for the change in enthalpy when considering changes in internal energy and pressure-volume work?
What is the correct expression for the change in enthalpy when considering changes in internal energy and pressure-volume work?
What happens to macroscopic properties of a system in thermal equilibrium over time?
What happens to macroscopic properties of a system in thermal equilibrium over time?
When separated by a diathermic wall, what indicates that two systems are in thermal equilibrium?
When separated by a diathermic wall, what indicates that two systems are in thermal equilibrium?
What happens to the volume of the gas when pressure on the piston, Pext, is increased by dP?
What happens to the volume of the gas when pressure on the piston, Pext, is increased by dP?
What is the formula for heat capacity when mass is considered as 1 mol?
What is the formula for heat capacity when mass is considered as 1 mol?
What type of heat capacity is indicated by the change in internal energy at constant volume?
What type of heat capacity is indicated by the change in internal energy at constant volume?
Which of the following units is applicable for heat capacity?
Which of the following units is applicable for heat capacity?
Which statement about heat and heat capacity is correct?
Which statement about heat and heat capacity is correct?
What type of molar heat capacity is determined at constant pressure?
What type of molar heat capacity is determined at constant pressure?
In the expression $dq = dE + p imes dV$, what does $dq$ represent?
In the expression $dq = dE + p imes dV$, what does $dq$ represent?
What is the mathematical relationship that defines heat capacity?
What is the mathematical relationship that defines heat capacity?
What is the expression for the work done by the gas during isothermal reversible expansion?
What is the expression for the work done by the gas during isothermal reversible expansion?
What is the relationship between pressure and volume in an ideal gas, as described by the ideal gas equation?
What is the relationship between pressure and volume in an ideal gas, as described by the ideal gas equation?
If the external pressure Pext is decreased, what is the effect on the gas?
If the external pressure Pext is decreased, what is the effect on the gas?
What is the mathematical form of work done by the gas in terms of pressure and volume change?
What is the mathematical form of work done by the gas in terms of pressure and volume change?
As per the derivation, what does the natural logarithm of the ratio of volumes indicate in the work equation?
As per the derivation, what does the natural logarithm of the ratio of volumes indicate in the work equation?
Which of the following expressions is used to relate pressures in the context of the ideal gas behavior?
Which of the following expressions is used to relate pressures in the context of the ideal gas behavior?
In the formula $W = - nRT ln\frac{P_2}{P_1}$, what does this expression represent?
In the formula $W = - nRT ln\frac{P_2}{P_1}$, what does this expression represent?
In the work done formula for reversible processes, what does the negative sign indicate?
In the work done formula for reversible processes, what does the negative sign indicate?
What do the terms $P_{ext}$ and $P_{gas}$ represent in the context of gas expansion?
What do the terms $P_{ext}$ and $P_{gas}$ represent in the context of gas expansion?
What is the role of the area (A) and the distance (dL) in calculating work done during gas expansion?
What is the role of the area (A) and the distance (dL) in calculating work done during gas expansion?
What is the value of entropy at absolute zero for a pure crystal?
What is the value of entropy at absolute zero for a pure crystal?
Which of the following describes standard entropy?
Which of the following describes standard entropy?
According to Hess's Law, what can be said about the total heat change in a chemical process?
According to Hess's Law, what can be said about the total heat change in a chemical process?
What is the standard entropy change ($ riangle S^ heta$) calculated from?
What is the standard entropy change ($ riangle S^ heta$) calculated from?
The absolute entropy of substances is always:
The absolute entropy of substances is always:
What is the primary application of Hess's Law?
What is the primary application of Hess's Law?
What does a positive value of $ riangle S^ heta$ indicate about a reaction?
What does a positive value of $ riangle S^ heta$ indicate about a reaction?
For which of the following is Hess's Law particularly useful?
For which of the following is Hess's Law particularly useful?
Flashcards are hidden until you start studying
Study Notes
Spontaneous Changes
- A spontaneous change is accompanied by a decrease in internal energy or enthalpy (ΔH)
Zeroth Law of Thermodynamics
- If two thermodynamic systems are separately in thermal equilibrium with a third object, they are in equilibrium with each other.
- Objects in thermodynamic equilibrium have the same temperature.
- A system in thermal equilibrium is a system whose macroscopic properties are not changing in time.
- Macroscopic Properties: Macroscopic properties of matter are properties that can be visible to the naked eye, i.e. Pressure, Temperature, Density, Volume, etc.
- Two systems are in thermal equilibrium when there is no net flow of thermal energy between them when they are connected by a path permeable to heat.
- Two substances/systems are in thermal equilibrium if when separated by a diathermic wall, there is no net energy transfer between them.
- A system is in thermodynamic equilibrium if there is no net change in its macroscopic properties with time.
- A system is in thermodynamic equilibrium if it is in mechanical, chemical, and thermal equilibrium.
- Systems in thermodynamic equilibrium are always in thermal equilibrium, but the converse is not always true.
First Law of Thermodynamics
- The total energy of an isolated system remains constant though it may change from one form to another.
- Mathematical Expression: H = E + PV
- Change in Enthalpy: ΔH = H2 – H1; ΔH = (ΔE) + (ΔPV); ΔH = (ΔE) + (PΔV); ΔH = (ΔE) + W; ΔH = q when change in state occurs at a constant pressure ΔH = qp
- Sign Conventions: ΔH is positive if H2>H1 and the process or reaction is endothermic. ΔH is negative if H2<H1 and the process or reaction is exothermic. ΔH = Hproducts – Hreactants = qp
- Units: kilocalories (kcal) or kilojoules (kJ)
Reversible Expansion
- The reversible expansion of the gas takes place in a finite number of infinitesimally small steps.
- Pext = Pgas = P
- Work done by the gas is expressed as: dW = P x A x dL; dW = P x dV
- The total amount of work done by the isothermal reversible expansion of the ideal gas from V1 to V2 is: W = − ∫ 𝑃 · 𝑑𝑉
- W = − 𝑛𝑅𝑇 ln 𝑉2/𝑉1
- W = − 𝑛𝑅𝑇 ln 𝑃1/𝑃2
- Isothermal compression work of an ideal gas is exactly the same value with the sign changed.
Concept of Heat Capacity
- Definition: Heat absorbed by unit mass in raising the temperature by one degree (K or ºC) at a specified temperature.
- Mathematical Expression: c = Q / [m × (T2 − T1)]
- C = Q / (T2 − T1) = ΔQ / ΔT
- C = dQ / dT
- Unit: cal K-1 mol-1 or J K-1 mol-1
- Heat is not a state function, neither is heat capacity.
Molar Heat Capacity at Constant Volume
- dQ = dE + 𝑝 · dV
- CV = dQ / dT = dE / dT
- Definition: Rate of change of internal energy with temperature at constant volume.
- Units: cal K-1 mol-1 or J K-1 mol-1 or eu (entropy units)
- A Process accompanied by an increase in entropy tends to be spontaneous.
Third Law of Thermodynamics & Absolute Entropy
- Statement: At absolute zero, the entropy of a pure crystal is also zero.
- S = 0 at T = 0 K.
- Absolute Entropy is the actual amount of entropy that a substance possesses at any temperature above zero K.
- Standard Entropy is the absolute entropy of a substance at 25ºC (298 K) and one atmosphere pressure.
- Absolute entropy of elements is zero only at 0 K in a perfect crystal.
- Standard entropies of all substances at any temperature above 0 K always have positive values.
- The standard entropy change ΔSº for chemical reactions can be calculated by: ΔSº = ΣSº(products) – ΣSº(reactants)
Hess’s Law
- Statement: If a chemical change can be made to take place in two or more ways whether in one step or two or more steps, the amount of total heat change is the same no matter by which method the change is brought about.
- Hess' Law of Constant Heat Summation is useful in the determination of:
- Heats of formation of unstable intermediates like CO(g) and NO(g).
- Heat changes in phase transitions and allotropic transitions.
- Lattice energies of ionic substances by constructing Born-Haber cycles if the electron affinity to form the anion is known.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
