Tricky Engineering Chemistry Questions and Answers focuses on “Phases and Components – 2”.
1. If a system has 7 solid species and 2 gaseous species, what is the number of phases present in the system?
a) 8
b) 7
c) 9
d) 6
Answer: a
Clarification: We know that n gaseous components contribute to one phase and n solid components contribute to n phases. Therefore, we have 7+1 = 8 phases in the given system.
2. If a system has n number of gaseous components, then what is the number of phases?
a) 0
b) 1
c) n
d) 1
Answer: d
Clarification: We know that n gaseous components contribute to one phase and n solid components contribute to n phases. Therefore, we have only one phase in the given system.
3. Calculate the degree of freedom for the following reaction.
2KClO3 ⟶ 2KCl + 3O2 (Gas)
a) 1
b) 2
c) 3
d) 0
Answer: a
Clarification: We know that the number of phases and components in the above reaction is 3 and 2 respectively. Since it is a one component system, F = C-P+2 = 2-3+2 = 1.
4. What is the formula for the Degree of Freedom for a condensed phase rule?
a) F=C-P+2
b) F=C-P+1
c) F=C+P+2
d) F=C+P+1
Answer: b
Clarification: Since for a condensed phase rule, the pressure is accounted as atmospheric pressure so that we can represent the system in 3D. Hence the formula reduces for condensed phase rule.
5. Calculate the number of phases in a mixture of water and oil.
a) 1
b) 2
c) 3
d) 4
Answer: b
Clarification: Though the system is a mixture of two liquids, they are immiscible and hence they should be considered as two different phases. Hence the number of phases is 2.
6. Calculate the number of phases in a saturated solution of NaCl and water.
a) 2
b) 1
c) 3
d) 4
Answer: a
Clarification: We know that salt is soluble in water. So normally the number of phases is one. But under saturated condition, salt becomes insoluble in water and so the number of phases is 2 (as they form heterogeneous mixture).
7. Calculate the number of phases in an unsaturated solution of NaCl and water.
a) 2
b) 1
c) 3
d) 4
Answer: b
Clarification: Since the salt is completely miscible in water, it forms a homogeneous mixture and hence it has only one phase (miscible liquids form only one phase and only one component).
8. Calculate the number of phases in Mohr salt.
a) 2
b) 3
c) 1
d) 0
Answer: c
Clarification: Mohr salt is (NH4)2Fe(SO4)2•6H2O. Since it is a single component (though it has many species), it has only one phase (a component with n species has only one compound).
9. What are the factors that affect phase rule?
a) Gravity
b) Electrical force
c) Magnetic force
d) Concentration
Answer: d
Clarification: Since phase rule is a property of a system, it only depends on factors like concentration, degree of freedom, solubility, equilibrium temperature, equilibrium pressure etc. (only stable factors are considered).
10. Calculate the number of phases in the transformation of rhombic to monoclinic sulphur.
a) 2
b) 1
c) 3
d) 4
Answer: a
Clarification: Since the system transforms from one form to another, under equilibrium, both the forms would exist together, and hence the system has 2 phases (under non-equilibrium, it has only one phase).
To practice Tricky questions and answers on all areas of Engineering Chemistry,