Thermodynamics Flashcards
Statement 1: The laws of thermodynamics deal with energy changes of microscopic systems rather than macroscopic systems containing a large number of molecules.
Statement 2: Laws of thermodynamics apply only when a system is in equilibrium or moves from one equilibrium state to another equilibrium
Statement 1 is incorrect and 2 is correct
The laws of thermodynamics deal with energy changes of macroscopic systems involving a large number of molecules rather than microscopic
systems containing a few molecules.
Statement 1:A system in thermodynamics refers to that
part of universe in which observations are
made and remaining universe constitutes
the surroundings.
Statement 2: system as separated from the
surroundings by some sort of wall which may
be real or imaginary called as boundary
Both statements are correct
Internal energy, U of the system may change, when
3 conditions
• heat passes into or out of the system,
• work is done on or by the system,
• matter enters or leaves the system.
Statement 1: W(adiab) is positive when work is done on the
system and the internal energy of system
increases.
Statement 2: if the work is done by the
system, W(adiabatic)will be negative because internal
energy of the system decreases.
Both statements are correct
Statement 1 q is positive, when heat
is transferred from the surroundings to the
system and the internal energy of the system
increases
Statement 2: q is negative when heat is
transferred from system to the surroundings
resulting in decrease of the internal energy of
the system.
Both statements are correct
∆U = q + w is
mathematical statement of the first law of
thermodynamics, which states that
The energy of an isolated system is……………
.
constant
Process or change is said to be
reversible, if 3 conditions
process could, at any moment,be reversed by an infinitesimal change.
process proceeds infinitely slowly by a series of equilibrium states
system and the surroundings are
always in near equilibrium with each other.
Statement 1:An extensive property is a
property whose value is independent of the quantity
or size of matter present in the system.
Statement 2: Properties which depend
on the quantity or size of matter present
are known as intensive properties.
Both statements are incorrect
Extensive: depend on quantity……..
Intensive: are independent of quantity……..
Assertion: For Water a lot of energy is needed to raise its temperature.
Reason: Water has a large heat capacity, When C is large, a given amount of heat results in only a small temperature rise.
Both assertion and reason are correct and reason correctly explain assertion
We define …………. As heat required to raise the temperature of one unit mass of a substance by one degree celsius (or one kelvin)
Specific heat capacity
We can measure energy changes associated
with chemical or physical processes by an
experimental technique called………..
calorimetry
Heat absorbed at constant………..is measured in a bomb
calorimeter
volume
Since the bomb calorimeter is sealed, its volume does not change so no………. Is done as the reaction is carried out at constant…………
Work
Volume
The standard enthalpy of reaction is the
enthalpy change for a reaction when all
the participating substances are in their………….
standard states.
The standard state of a substance at a
specified temperature is its pure form at pressure………
1 bar
The enthalpy change that accompanies
melting of one mole of a solid substance in
standard state is called…………….
standard enthalpy
of fusion or molar enthalpy of fusion,
∆fusH
Amount of heat required to vaporize one
mole of a liquid at constant temperature
and under standard pressure (1bar) is called
its…………
standard enthalpy of vaporization or
molar enthalpy of vaporization,
.
………………is the change in enthalpy when one mole of a solid substance sublimes at a constant temperature and under standard pressure (1bar).
Standard enthalpy of sublimation, subH
Assertion: Thus, it requires less heat to vaporise 1 mol of acetone than it does to vaporize 1 mol of water.
Reason: The magnitude of the enthalpy change depends on the strength of the intermolecular interactions in the substance undergoing the phase transfomations.
Both are correct and R is correct explanation of A
the strong hydrogen bonds between water molecules hold them tightly in liquid phase.
For an organic liquid, such as acetone, the intermolecular dipole-dipole interactions are significantly weaker.
The standard enthalpy change for the formation of one mole of a compound from its elements in their most stable states of aggregations is called………….
standard molar enthalpy of Formation.
By convention, standard enthalpy for formation, of an element in reference state, i.e., its most stable state of aggregation is taken as.
zero
A balanced chemical equation together with the value of its ∆r H is called a…………
thermochemical equation
If a reaction takes place in several steps then its standard reaction enthalpy is the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at the same temperature.
True or false
True
………………… is defined as the enthalpy change per mole (or per unit amount) of a substance, when it undergoes combustion and all the reactants and products being in their standard states at the specified temperature.
Standard enthalpy of combustion
Cooking gas in cylinders contain mostly……….
Butane
Combustion of glucose gives out………..of heat
2802kJ/mole
It is the enthalpy change on breaking one mole of bonds completely to obtain atoms in the gas phase.
Enthalpy of atomisation
The……………..is the change in enthalpy when one mole of covalent bonds of a gaseous covalent compound is broken to form products in the gas phase.
bond dissociation enthalpy
The…………..of an ionic compound is the enthalpy change which occurs when one mole of an ionic compound dissociates into its ions in gaseous state
lattice enthalpy
Ionization energy and electron affinity are defined at absolute zero. At any other temperature, heat capacities for the reactants and the products have to be taken into account
True or false
True
……………..of a substance is the enthalpy change when one mole of it dissolves in a specified amount of solvent
Enthalpy of solution
………….. at………….dilution is the enthalpy change observed on dissolving the substance in an infinite amount of solvent when the interactions between the ions (or solute molecules) are negligible.
The enthalpy of solution
infinite
For most of the ionic compounds, ∆solH is………and the dissociation process is………..
positive
endothermic
Assertion: Many fluorides tend to be less soluble than the corresponding chlorides
Reason: If the lattice enthalpy is very high, the dissolution of the compound may not take place at all.
Both are correct and R is correct explanation of A
As more and more solvent is used, the enthalpy of solution approaches a limiting value, i.e, the value in infinitely dilute solution.
True or false
True
…………… means ‘having the potential to proceed without the assistance of external agency’. However, it does not tell about the………….
spontaneity
rate of the reaction or process.
A…………..process is an irreversible process and may only be reversed by some external agency.
spontaneous
In an isolated system, there is always a tendency for the systems’ energy to become more…………..
disordered or chaotic
Statement 1:Temperature is the measure of average chaotic motion of particles in the system.
Statement 2: Heat added to a system at lower temperature causes lesser randomness than when the same quantity of heat is added to it at higher temperature.
Statement 1 is correct but statement 2 is incorrect
Heat added to a system at lower temperature causes greater randomness than when the same quantity of heat is added to it at higher temperature.
Statement 1: If the system is in thermal equilibrium with the surrounding, then the temperature of the surrounding is same as that of the system.
Statement 2: But increase in enthalpy of the surrounding is not equal to decrease in the enthalpy of the system.
Statement 1 is correct but 2 is incorrect
increase in enthalpy of the surrounding is equal to decrease in the enthalpy of the system.
Assertion: Exothermic reactions are spontaneous in nature
Reason: In exothermic reactions heat released by the reaction increases the disorder of the surroundings and overall entropy change is positive which makes the reaction spontaneous.
Booth are correct and R is correct explanation of A
Assertion: The entropy of any pure crystalline substance approaches zero as the temperature approaches absolute zero. This is called third law of thermodynamics.
Reason: This is so because there is perfect order in a crystal at absolute zero.
Both are correct and R is correctly explanation of A
Assertion: Statement of third law of thermodynamics is confined to pure crystalline solids only
Reason: theoretical arguments and practical evidences have shown that entropy of solutions and super cooled liquids is not zero at 0 K.
Both are correct and R is correct explanation of A
In case of compression the work done in………… process is less than done in…………..
Reversible
Irreversible
Irreversible > reversible
Opposite for expansion
Assertion:In case of expansion maximum amount of work is obtained by reversible process
Reason: Less heat is lost to the surrounding
Both are correct and R is correct explanation of A
If question says isoenthalpic process then work………
Work is Pext*V
The free energy change (AG°) is negative when -
1. The surroundings do no electrical work on the system.
2. The surroundings do electrical work on the system.
3. The system does electrical work on the surroundings.
4. The system does no electrical work on the surroundings.
3 is correct
Closed system characteristics
This type of system can exchange energy in the form of heat, work or radiations but not matter with its
surroundings.
Boundary is sealed but not insulated
Isolated system
This type of system has no interaction with its surroundings. Neither matter nor energy can be exchanged with surroundings.
The boundary is scaled and is insulated.
Open system characteristics
Exchange of matter as well as energy takes place
Boundary is neither insulated nor sealed
Irreversible process
This process is not carried out infinitesimally slowly but is carried out rapidly rapidly ie. the difference between the driving force and the opposing force is quite large.
Equilibrium may exist only after the completion of the process.
Takes finite time for completion
Actually occur in nature
Reversible process
Carried out in infinitesimally small steps
Difference between driving force and opposing force is very small
At any stage during the process false equilibrium is not distributed
Takes infinite time for completion
Only imaginary and can’t be achieved in reality
Assertion: Entropy of propane is more than ethane
Reason: Entropy of complex molecules is greater than simpler molecules
Both are correct and correct explanation
More complex the molecule is more are the ways of arranging atoms in 3D
Assertion: Entropy of NaF is greater than MgO
Reason: Entropies of ionic solids become larger as the attraction amongst the ions become weaker
Both are correct and correct explanation
Charge in MgO both have +2 and -2 respectively thus greater attraction and lesser entropy
Assertion: Entropy of C (diamond)<C(graphite)<Fe<Al<Na
Reason: Entropy of harder substance is smaller than softer substances
Both are correct and correct explanation
Assertion: Entropy increases on boiling an egg
Reason: Protein bonds get broken and denaturation of proteins takes place
Both are correct and correct explanation
Process of snow formation is an……………reaction. But, snowfall will be an……….process.
exothermic
endothermic
