Chemistry Test 170

Explanation of Equilibrium in Closed System

• Understanding Equilibrium: Equilibrium is a state in which opposing forces or influences are balanced. In terms of thermodynamics, it refers to a state where all the processes occur at the same rate in the forward and backward directions, making the overall macroscopic properties of the system unchanged.
• Equilibrium in Closed System: Equilibrium can be attained in a closed system because the energy exchange can occur until the system's properties reach a balance. For instance, chemical equilibrium or thermal equilibrium can be achieved in a closed system.
• Not in Open or Isolated Systems: In open systems, matter and energy can be exchanged with the surroundings, disturbing the balance. Isolated systems, on the other hand, and cannot exchange energy or matter with the surroundings, so they cannot reach equilibrium with their surroundings.

In conclusion, a closed system is best suited for achieving equilibrium as it allows for the necessary adjustments through energy exchange while maintaining a constant matter within the system.The equilibrium state can only be reached if the chemical reaction takes place in a closed system. Otherwise, some of the products may escape, leading to the absence of a reverse reaction.

The correct answer is Na.

The decreasing order of atomic radius is Na (227pm) > P (195pm) > S (180pm) > Cl (175pm).

Therefore,

When two atoms have the same value of n for the valence electrons, the atom with the greater number of protons will generally have a greater effective nuclear charge to draw the valence electrons closer to the nucleus and, thus, decrease the atomic radius. 

Since chlorine's 17 protons are greater than sodium's 11 protons, chlorine will have a greater effective nuclear charge to draw chlorine's valence electrons closer to the nucleus and, thus, chlorine is expected to have a smaller atomic radius.

While sodium with the lower effective nuclear charge is expected to have a larger atomic radius.

This law of multiple proportions is also known as Dalton's law because this law was announced (1803) by the English chemist John Dalton.

Law of multiple proportions:

if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.

Hydrogen combines with oxygen to form two compounds, water and hydrogen peroxide.

Hydrogen + Oxygen → Water
      2g             16g          18g
Hydrogen + Oxygen → Hydrogen Peroxide
      2g             32g          34g

Masses of oxygen is16 g (in water) and 32 g (in hydrogen peroxide) combine with 2g of hydrogen, bear a simple ratio, 16:32 or 1: 2.

The law of mass action states that the rate of reaction is proportional to the product of the molar concentration of reactant with each concentration term raised to power its stoichiometric coefficient.

In a chemical reaction a state comes when both the forward and reverse reactions occur at the same rate and this state is known as equilibrium. At the beginning of the reaction, the rate of the Forward reaction is higher than the rate of backward reaction.

Understanding Dynamic Equilibrium

Dynamic equilibrium refers to a state of balance achieved by two processes occurring at the same rate. In the context of chemical reactions, it describes a condition where the rate of the forward reaction is equal to the rate of the backward reaction.

At dynamic equilibrium, the concentrations of the reactants and products do not change because the rates of the forward and backward reactions are the same. This is a state of balance, but not necessarily a state of equality.

Difference in Concentrations of Reactants and Products

The concentrations of reactants and products at dynamic equilibrium are not necessarily equal. They are constant, but not necessarily the same.

The relative concentrations of the reactants and products at equilibrium depend on the specifics of the reaction, including the equilibrium constant.

The equilibrium constant, represented as K, is the ratio of the concentrations of the products to the reactants at equilibrium. If K is greater than 1, the concentration of the products is greater than the reactants at equilibrium. If K is less than 1, the concentration of the reactants is greater than the products at equilibrium.

EDTA:

EDTA stands for ethylene diamine tetraacetate.

It is a hexadentate ligand, which means a single molecule can occupy six stereochemical positions around a metal atom.

Hence, the coordination number of EDTA is six.

The structure of EDTA is:

​

As EDTA is a polydentate ligand, it is also a chelating ligand, it contains donor atoms so arranged that they can occupy more than one position around the same metal atom simultaneously in the first sphere of coordination.

The resulting complexes are called chelates. Example of chelate complexes are:

​

Hence, EDTA has a coordination number is six.

400 ppm means 400 gm of CaCO₃ are present per 1000000 L of solution.

Hence, we can say 0.4 gm of CaCO₃ are present per litre of solution.

Molarity is defined as no. of mole of solute of solute present per litre of solution.

So, M = 0.4 / molar mass of CaCO₃

M = 4 X 10^-3

Hence, the correct option is (3).

Key Points

A deposition is a process by which a gas is converted into a solid.

Sublimation is the process by which a solid is converted to gas directly without changing into liquid in between.

Vaporisation is the process of conversion of a solid or liquid into a gas (vapor).

Freezing is a process of conversion of liquid into solid at the freezing point.

A generalisation made by the English chemist J.A.R. Newlands in 1865 that, if the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties will appear after each interval of seven elements, which is a generalisation of the law of octaves.