Every aspirant wants admission in the best engineering college by securing good rank in engineering entrance examinations. Aspirants will have to focus on all subjects if they want to secure good rank in the examination. Students should try to prepare notes of all the chapters of all subjects during their preparation for the examination.
To help aspirants to score good marks in coming WBJEE 2018, the engineering section bring to you the notes of chapter Thermodynamics. Students always get 1-2 questions from this chapter in the examination.
Students can read the following topics here:
1. System and Surroundings,
2. Types of system (open, closed, isolated),
3. State variables/functions,
4. Thermodynamic processes (isothermal, adiabatic, isobaric, isochoric),
5. Sign conventions,
6. Extensive and Intensive properties,
7. Enthalpy and Entropy,
8. Gibbs free energy,
9. First law of thermodynamics,
10. Relationship between C_{p} and C_{v},
11. Standard enthalpy of reactions,
12. Enthalpy changes during phase transformations,
13. Properties of enthalpy changes,
14. Hess's law of constant heat summation and
15. Calorimetry
About the notes:
1. These notes are based on the latest syllabus and pattern of WBJEE entrance examination.
2. These notes are prepared by Subject Experts of Chemistry.
3. Some previous years’ solved questions are also included here which will help aspirants to get familiar with the difficulty level of the questions asked in the previous years’ paper of WBJEE test.
Important Concepts:
The System and the Surroundings
The Universe = The system + The surroundings
Types of the System
Mathematically, ΔE ≠ 0 and Δm ≠ 0
Mathematically, ΔE ≠ 0 and Δm = 0
Mathematically, ΔE = 0 and Δm = 0
State variables / State functions: The functions whose values depend only on the state of the system and not on how it is reached are called state functions.
Thermodynamics Processes:
Mathematically, ΔT = 0
Mathematically, q = 0
Mathematically, Δp = 0
Mathematically, ΔV = 0
Sign Conventions
For ex: heat given to system or work done on system is taken as positive
For ex: heat given out by the system or work done by system is taken negative
Extensive and Intensive Properties
Example: temperature, density, pressure
Example: mass, total volume
Standard enthalpy of reactions: It is the enthalpy change for a reaction when all the participating substances are in their standard states.
Enthalpy changes during phase transformations:
Properties of Enthalpy Change:
WBJEE: Important Questions and Preparation Tips – Atomic Structure
Some previous years' solved questions are given below:
Question 1:
For the reaction X_{2}Y_{4}(I) → 2 XY_{2}(g) at 300 K the values of ΔU and ΔS are 2 kCal and 20 Cal K^{–1} respectively. The value of ΔG for the reaction is
(A) – 3400 Cal
(B) 3400 Cal
(C) – 2800 Cal
(D) 2000 Cal
Solution 1:
We have the reaction,
X_{2}Y_{4}(I) → 2 XY_{2}(g)
Hence, the correct option is (C).
WBJEE: Important Questions and Preparation Tips – Basic Concepts of Chemistry
Question 2:
The condition for a reaction to occur spontaneously is
(A) ΔH must be negative
(B) ΔS must be negative
(C) (ΔH-TΔS) must be negative
(D) (ΔH+TΔS) must be negative
Solution 2:
When ΔG<0 then the reaction occur spontaneously.
Also, ΔG= ΔH-TΔS
So, for spontaneous reaction ΔH-TΔS should be negative.
Hence, the correct option is (C).
Question 3:
Which of the following plots represent an exothermic reaction ?
For example,
Solution 3:
We know that,
Hence, the correct option is (D).
WBJEE: Important Questions and Preparation Tips – States of Matter
Students can also have a look on the following questions and solutions to check their preparation.
Question 1:
Solution 1:
The criterion for spontaneity of any process the change in entropy is (ΔS_{system} + ΔS_{surrounding ) > 0.}
Hence, the correct option is (D).
Question 2:
The species which by definition has zero standard molar enthalpy of formation at 298 K is
(A) Br_{2}(g)
(B) Cl_{2}(g)
(C) H_{2}O(g)
(D) CH_{4}(g)
Solution 2:
Elements in its standard state have zero enthalpy of formation. Since, Cl_{2} is gas at room temperature, therefore ΔH° of Cl_{2}(g) is zero.
Hence, the correct option is (B).
Question 3:
Which of the following statements is false?
(A) Work is a state function
(B) Temperature is a state function
(C) Change in the state is completely defined when the initial and final states are specified
(D) Work appears at the boundary of the system
Solution 3:
Work is not an example of state function.
Hence, the correct option is (A).
Question 4:
In thermodynamics, a process is called reversible when
(A) Surroundings and system change into each other
(B) There is no boundary between system and surroundings
(C) The surroundings are always in equilibrium with the system
(D) The system changes into the surroundings spontaneously
Solution 4:
When the surroundings are always in equilibrium with the system, then the process is called reversible process.
Hence, the correct option is (C).
Conclusion:
Students can easily understand this chapter as the content given here is arranged in a systematic manner. Students can also track their progress by attempting the questions given here. They can also refer the solutions if they stuck somewhere while attempting the paper.
WBJEE 2018: Notification, Application, Dates, Eligibility, Exam Pattern, Syllabus
WBJEE 2018: Exam Pattern, Important Questions, Previous Years’ Solved Papers and Preparation Tips
How to crack WBJEE in 1 month? Strategy based on the differences between JEE and WBJEE
WBJEE 2018: Application Form, Important Dates, Syllabus and Eligibility
WBJEE Solved Mathematics Question Paper 2015