11. Thermodynamics (8 lectures) Flashcards
What is thermodynamics?
Thermodynamics - branch of physical chemistry concerned with studying the transformations of E (heat -> work)
What are the common units of measure in thermochemistry?
What are the formulas for force, pressure, energy
EKE- movement of particles
Epot - E stored in bonds
How to calculate the total work done when a force graph is given?
Integration of the graph
How can temperature in C be converted into K?
Explain thermal equilibrium and zeroth law of thermodynamics
What is an intensive property?
Explain the Ideal Gas Law
pV = nRT
Real gases show ideal gas properties (obey Boyle’s law) as p reaches 0 => example of limiting law
What is the Ideal Gas Law based on? Explain the concept
Boyle’s law; Charles’s law; Avogadro’s principle:
As V is decreased - p increases
As V is increased - p decreases
As temperature increased - p increases (V unchanged)
As temperature decreases - p decreases (V unchanged)
All gases of same amount at STP are of the same volume
Explain what are SATP conditions and what are the units of the gas constant
Define the Ideal Gas
Explain Dalton’s law (mixtures of ideal gases)
How to calculate partial pressures in gas mixtures?
How is heat, work and internal E related? (First Law of Thermodynamics)
What is the difference between the system and its surroundings?
What is the difference between heat and work?
Explain what is work and how it relates to force
V1 - initial volume
V2 - final volume
Minus before the integral because - E leaves the system (w<0)
Plus before an integral would be when - E enters the system (w>0)
What is irreversible work? Explain
Gas expands without any loss of heat to the surrounding
What is mechanical equilibrium? Explain
The system does the least amount of work (w) when the external pressure (pex) is 0
What is the relation between mechanical equilibrium and reversibility?
What is isothermal reversible gas expansion?
Compare and contrast the calculation and graphs of work done at constant external pressure and reversible isothermal expansion
Explain heat, heat capacity and latent heat: heat is supplied to raise T
How does specific heat capacity / molar heat capacity differ from heat capacity?
What is internal energy?
How to calculate internal energy? What is the differences between heat/work when it enters/leaves the system?
What is a state function?
How does the First Law of Thermodynamics related to internal E?
How does the internal E change be measured experimentally?
What is enthalpy?
How can reactions be classified depending on enthalpy change?
Define thermochemistry, what is the technique used to determine changes?
Enthalpy
State function - does not depend on the path taken to reach the outcome
Name the physical phase changes in matter in endothermic and exothermic reactions
Why is enthalpy of vaporisation in water high and why it is useful?
H bonds - many of them
Controls temperature in the planet
What is the enthalpy of fusion? What is the opposite of it?
E required as heat at constant p to convert 1 mol of solid into liquid phase
ΔfusH = .. kJ mol-1
Enthalpy of vapourisation is the oppsoite of enthalpy of fusion
When are the reverse reactions of the same enthalpy? How are fusion, vaporisation and sublimation related?
At same pressure and temperature
Explain enthalpy of ionisation, enthalpy of e gain, lattice enthalpy change and hydration enthalpy
Explain enthalpy of solution: solution, hydration and lattice
What is the enthalpy of chemical change? What are the variables on which it depends?
Explain enthalpy of combustion
Excess O2
Reaction produces heat and work (example)
Explain what is Hess’s law
What is the driving force of spontaneous / non-spontaneous reactions?
Spontaneous - tendency of matter to be disordered
Non-spontaneous - work
Explain the disperse of E and the idea behind it
Explain the Second Law of Thermodynamics
What is the equation to measure entropy chnage? Explain why ΔS is proportional to q, inversely proportional to T and qrev used
- proportional to q because - transfer E as heat increases the random motion of particles → increase in disorder
- inversely proportional to T because - if object is hot the change in disorder will be less significant than the change in disorder in a cold object
- qrev because - the studied system is in thermal and mechanical equilibrium - the distribution of matter is not random
Explain Trouton’s rule, wht are NH3 and H2O different?
What are the possible ways to change entropy in a system?
- Change in V (ΔS = nRln(V2/V1) = -nRln(p2/p1) )
- Phase transition (ΔS = qrev / T = ΔHtr / Ttr )
- Heating (ΔS = cln(T2/T1) )
What object could have an entropy value of 0? State the Third Law of Thermodynamics
A perfectly ordered system, ex a solid crystal at 0 K temp
IN reality perfect crystal cannot be achieved
Explain standard reaction entropy and its formula
Explain entropy of mixing
Calculated by the expansion formula for
ΔS = nRln(V1/V2)
Entropy change in a system vs in surrounding
- Entropy change in system: entropy of mixing
- Entropy change in surrounding: E transfer from system to surrounding (ex as heat)
What is the enthalpy of the universe? How does it determine spontaneity of a reaction?
Enthalpy of the universe is equal to the sum of enthalpies for the system and its surrounding
ΔS > 0 → irreversible spontaneous reaction
ΔS = 0 → reversible change (at equilibrium)
ΔS < 0 → irreversible non-spontaneous reaction (sito nesake taip tiesiogiai, deducinau)
Whats is Gibbs energy used for?
To describe spontaneity of a process at a constant temperature and pressure
Explain Gibbs energy and the meanings of its values
What is the standard Gibbs energy change? What conditions must be met for it to be standard?
What is phase transition and what does Gibbs energy equal to?
- Phase transition: transitions between allotropes, (ex tin pest: beta tin to alpha tin; maleable form to brittle)
- Gibbs E at phase change = 0 → equation can be used to determine temperature
How does Gibbs energy change through the reaction?
How should the graph of Gibbs E diagram be interpreted for a reaction?
When is a system at equilibrium?
No tendency to spontaneously occur in neither direction
What does the value K tell about the reaction?
How does Q and K of a reaction relate?
What is the effect of tempreature on equilibrium constant K?
As themperature is raised → K increases because more products are formed (K = [products]/[reactants])
What does the van’t Hoff equation do?
Allows to calculate K2 at a different T2 when K1 and T1 is known
How can van’t Hoff equation be used to predict K value when temperature is altered in an endothermic process?
In exothermic the opposite
Is K dependent on pressure?
No but change in pressure changes the position of equilibrium in the reaction (K is a constant)
