Learning Objectives:

• Define and use the concept of a mole.
• Use the mole concept to calculate the number of atoms, ions or molecules in a sample of material.
• Calculate percent composition and empirical and molecular formula.
• Perform Stoichiometric calculations including determination of mass relationships between reactants and products.

Stoichiometry is the study of the quantitative aspects of chemical reactions. It deals with the numerical relationships of elements and compounds and the mathematical proportions of reactants and products in chemical transformations.

Mole is defined as that quantity of a substance that contains the same number of ultimate particles (atom, ions or units of ions) as present in 12 grams of Carbon (C-12).

Molecular mass equals the sum of atomic masses of all atoms in the molecule. The unit of molecular mass is amu.

Molar mass is the sum of masses of the atoms present in one mole of a substance, which can be an element or a compound. It can be expressed as a unit of mass per mole like grams/mol, kg/mol

Avogadro's number: The number of molecules in a mole of any particular substance is the same as the number of atoms in a gram-atom of any number. This number of atom is called the Avogadro's number, the accepted value of which is 6.02 $\times$ 10$^{23}$.

Solved Example: 9180-01

Which one of the following has different number of molecules? (All kept at normal temperature and pressure)

A. 3 gram of Hydrogen

B. 48 gram of Oxygen

C. 42 gram of Nitrogen

D. 2 gram of Carbon

Correct Answer: D

Solved Example: 9513-01

What is the purpose of stoichiometry in chemistry?

A. To determine the color of a reaction

B. To study the physical properties of substances

C. To establish the relationship between reactants and products in a chemical reaction

D. To calculate the boiling point of a substance

Correct Answer: C

Solved Example: 9513-02

In the reaction \[CH_4+2 O_2 \rightarrow CO_2 + 2 H_2O \] if 16 grams of methane (CH$_4$) react, how many grams of water (H$_2$O) will be produced?

A. 18 g

B. 36 g

C. 54 g

D. 72 g

\[CH_4+2 O_2 \rightarrow CO_2 + 2 H_2O \] 1 mole of CH$_4$ produces 2 moles of H$_2$O.
16 g of CH$_4$ produces 2 $\times$ 18 = 36 g of H$_2$O.

Correct Answer: B

Learning Objectives:

• Understand how concentrations change over time for reactants and products over time in a chemical equilibrium reaction.
• Calculate equilibrium constants as a ratio between the concentrations of the reactants and the concentration of the products.

• A reaction which can go in forward and backward direction simultaneously is called reversible reaction.
• In a system at equilibrium, both orward and reverse reactions are running simultaneously. The conversion between reactants and products is depicted by a double arrow.
\[CaCO_3 \rightleftharpoons CO_2 + CaO \]
• In chemical equilibrium the concentrations of reactants and products remain constant over time.
• At equilibrium the forward and reverse reactions are proceeding at the same rate.

Equilibrium Constant of a Chemical Reaction: \[aA + bB \rightleftharpoons cC + dD\]

$K_{EQ} = \dfrac{[C]^c[D]^d}{[A]^a[B]^b}$       Page 85

Fintelia, CC BY-SA 3.0, via Wikimedia Commons

Solved Example: 9187-01

Identify the equilibrium in which K$_c$ has no units:

A. Decomposition of HI

B. Decomposition of PCl$_5$

C. Decomposition of NH$_3$

D. Decomposition of CaCO$_3$

When the total number of moles of products is equal to the total number of moles of reactants, then K$_c$ has no units. \[2HI \rightleftharpoons H_2 + Cl_2\] \[PCl_5 \rightleftharpoons PCl_3 + Cl_2\] \[2NH_3 \rightleftharpoons N_2 + 3H_2\] \[CaCO_3 \rightleftharpoons CaO + CO_2\]

Correct Answer: A

Solved Example: 9187-02

What can affect the magnitude of equilibrium constant Kp of a reversible gaseous reaction:

A. Temperature

B. Pressure

C. Catalyst

D. None of above

Correct Answer: B

Solved Example: 9515-01

In a chemical reaction at equilibrium, which statement is true?

A. The concentration of reactants is equal to the concentration of products.

B. The reaction has stopped.

C. The forward and reverse reactions are occurring at the same rate.

D. The temperature of the system is constant.

Correct Answer: C

Solved Example: 9515-02

How does an increase in temperature affect the equilibrium position of an endothermic reaction?

A. The equilibrium shifts to the left.

B. The equilibrium shifts to the right.

C. The equilibrium position remains unchanged.

D. It depends on the specific reaction.

Correct Answer: B

Solved Example: 9515-03

If a catalyst is added to a reaction at equilibrium, what happens to the equilibrium position?

A. The equilibrium shifts to the left.

B. The equilibrium shifts to the right.

C. The equilibrium position remains unchanged.

D. The reaction stops.

Correct Answer: C

Learning Objectives:

• Define bioconversion and its role in converting renewable biological materials into useful products, such as biofuels, enzymes, and pharmaceuticals.

Bioconversion is the conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms, some detritivores or enzymes. (source: Wikipedia) ioconversion is a bioprocess that utilizes microorganisms (bacteria, yeasts, fungi) or enzymes to transform renewable biological materials into valuable products. It plays a significant role in industries like biofuels, pharmaceuticals, food production, and bioremediation.

Solved Example: 9203-01

The energy releases from glucose in presence of oxygen is called as:

A. Aerobic respiration

B. Anaerobic respiration

C. Fermentation

D. None of these.

Correct Answer: A

Solved Example: 9516-01

Which of the following is an example of bioconversion?

A. Combustion of coal

B. Fermentation of sugars to produce ethanol

C. Electrolysis of water

D. Oxidation of metals

Correct Answer: B

Solved Example: 9516-02

In the context of bioconversion, what is the role of enzymes?

A. To provide structural support to cells

B. To catalyze biochemical reactions

C. To transport nutrients across cell membranes

D. To store genetic information

Correct Answer: B