Definitions [1]
Define the Enthalpy of atomization.
The enthalpy change accompanying the dissociation of all the molecules in one mole of gaseous substance into atoms is called enthalpy of atomization.
Formulae [1]
Write the mathematical equation of the first law of thermodynamics for an isochoric process.
By substituting equation W = −pex . ΔV in the equation ΔU = q + W, we get
ΔU = q − pex . ΔV ...(1)
If the reaction is carried out in a closed container so that the volume of the system is constant, then Δ = 0. In such a case, no work is involved.
The equation (1) becomes ΔU = qv
Equation (1) suggests that the change in internal energy of the system is due to heat transfer. The subscript v indicates a constant volume process. As U is a state function, qv is also a state function. We see that an increase in the internal energy of a system is numerically equal to the heat absorbed by the system in a constant volume (isochoric) process.
Theorems and Laws [2]
Write the mathematical equation of the first law of thermodynamics for an isochoric process.
By substituting equation W = −pex . ΔV in the equation ΔU = q + W, we get
ΔU = q − pex . ΔV ...(1)
If the reaction is carried out in a closed container so that the volume of the system is constant, then Δ = 0. In such a case, no work is involved.
The equation (1) becomes ΔU = qv
Equation (1) suggests that the change in internal energy of the system is due to heat transfer. The subscript v indicates a constant volume process. As U is a state function, qv is also a state function. We see that an increase in the internal energy of a system is numerically equal to the heat absorbed by the system in a constant volume (isochoric) process.
State and explain Hess’s law of constant heat summation.
Hess’s law of constant heat summation states that, “The change in enthalpy for a reaction is the same whether the reaction takes place in one or a series of steps.”
The Hess’s law is a direct consequence of the fact that the enthalpy is a state function, and so the enthalpy change depends only on the initial and final states of the system and not on the path by which the reaction takes place.
Example: The conversion of A to C can take place directly
in a single step.
A → C, ΔH° = ΔH1
The reaction can also proceed in two steps, for which the ΔH° values are known.
Step (1): A → B, ΔH° = ΔH2
Step (2): B → C, ΔH° = ΔH3
______________________________
Overall: A → C, ΔH° = ΔH2 + ΔH3
According to Hess’s law, ΔH1 = ΔH2 + ΔH3. The sequence of steps is represented in the figure.
Important Questions [53]
- Write Features of Reversible Process.
- Write the Conditions for Maximum Work Done by the System.
- Distinguish Between Isothermal Process and Adiabatic Process.
- The Process in Which the Value of δU = 0 is __
- For a Certain Reaction, ∆H = − 50 Kj and ∆S = − 80 J K-1, at What Temperature Does the Reaction Turn from Spontaneous to Non-spontaneous?
- Which of the Following Pairs is an Intensive Property?
- Determine whether the reactions with the following ΔH and ΔS values are spontaneous or non-spontaneous. State whether the reactions are exothermic or endothermic.
- Derive the equation : W = - PextAV
- 5 Moles of Helium Expand Isothermally and Reversibly from a Pressure 40 × 10-5 N M-2 to 4 × 10-5 N M-2 at 300 K. Calculate the Work Done, Change in Internal Energy and Heat Absorbed During
- What is the action of heat on potassium permanganate?
- Absolute Entropies of Solids, Liquids and Gases Can Be Determined by
- 300 M mol of perfect gas occupies 13 L at 320 K. Calculate the work done in joules when the gas expands
- One Mole of a Gas Expands by 3l Against a Constant Pressure of 3 Atmosphere. Calculate the Work Done
- 55 L Atm of Work is Obtained When 1.0 Mole of an Ideal Gas is Compressed Isothermally from a Volume of 28.5 L to 18.5 L, the Constant External Pressure is
- For a Chemical Reaction, A→ Products, the Rate of Reaction Doubles When the Concentration of ‘A’ is Increased by a Factor of 4, the Order of Reaction is
- Derive an expression for maximum work in isothermal reversible expansion of two moles of an ideal gas.
- Write the mathematical equation of the first law of thermodynamics for an isochoric process.
- Write mathematical equation of first law of thermodynamics for Adiabatic process
- Write one statement of first law of thermodyamics and its mathematical expression
- Calculate the internal energy at 298K for the formation of one mole of ammonia, if the enthalpy change at constant pressure is – 42.0 kJ mol-1. (Given: R = 8.314 J K-1 mol-1)
- Prove that ΔH=ΔU+ΔnRT. what is the condition under which ΔU=ΔH?
- What will happen to the internal energy if work is done by the system?
- How is Enthalpy of Sublimation Related to Enthalpy of Fusion and Enthalpy of Vaporization
- Define the Enthalpy of Fusion
- Define the Enthalpy of atomization.
- If the Enthalpy of Vaporisation of Water at 100oc is 186.5 J.Mol-1, the Entropy of Vaporization Will Be
- For a chemical reaction ΔS=0.035 kJ/k and ΔH=20kJ.
- A system absorbs 640 1 heat and does work of 260 J, the change in internal energy of the system will be
- Define the Term ‘Enthalpy’.
- Define Enthalpy of Vaporization
- A System Absorbs 6 Kj of Heat and Does 1.5 Kj of Work on Its Surroundings. the Change in Internal Energy is
- Hess’s law of constant heat summation
- State and explain Hess’s law of constant heat summation.
- Calculate ΔH° for the reaction between ethene and water to form ethyl alcohol from the following data
- Calculate the Standard Enthalpy of the Reaction,From the Following δH° Values
- Calculate ∆H° for the Following Reaction: 2h3bo3(Aq) → B2o3(S) + 3h2o(L) Given That,
- Calculate C-Cl bond enthalpy from following reaction: CH3Cl(g) + Cl2(g) → Ch2Cl2(g) + HCl(g) ΔH° = -104KJ
- Calculate the standard enthalpy of combustion of CH3COOH(l) from the following data:
- For the Reaction: Cl2(G) → 2cl(G)
- Define Enthalpy of Sublimation.
- Calculate the Work Done in the Following Reaction at 50o C. State Whether Work is Done on the System Or by the System.
- The Standard Enthalpy of Combustion of Formaldehyde δ0h0 = -571 Kj. How Much Heat Will Be Evolved in the Formation of 22 G of Co2?
- Write Applications of Standard Molar Entropy.
- A Substance Which Shows the Highest Entropy is ___________.
- What Are the Conditions for Spontaneous and Non-spontaneous Reactions in Terms of Free Energy Change?
- Write Chemical Reactions Involved in Van Arkel Method for Refining Titanium
- The equilibrium constant Kp for the reaction, H2(g) + I2(g) → 2HI(g) is 130 at 510 K.
- Explain the Relationship Between Gibb'S Standard Energy Change of the Reaction and Equilibrium Constant.
- Amongst the Following Identify the Criterion for a Process to Be at Equilibrium
- Derive the relation between ΔG° and equilibrium constant (K) for the reaction - aA_bB ⇌ cC+dD.
- Give Two Uses Of Third Law of Thermodynamics
- State Third Law of Thermodynamics
- No Machine Has an Efficiency Unity', is Stated In-
Concepts [17]
- Chemical Thermodynamics and Energetic
- Concepts of System
- Types of Systems
- Surroundings
- Work, Heat, Energy, Extensive and Intensive Properties
- State Functions
- First Law of Thermodynamics
- Internal Energy and Enthalpy
- Hess’ Law of Constant Heat Summation
- Enthalpy of Bond Dissociation
- Combustion, Formation, Atomization, Sublimation
- Phase Transition
- Ionization and Solution
- Dilution Introduction of Entropy as a State Function
- Free Energy Change for Spontaneous and Non Spontaneous Processes
- Equilibrium Constant
- Second and Third Law of Thermodynamics
