Comprehensive NEET Chemistry Elements and Periodicity in Properties Formula Summary

1. Stoichiometry and Chemical Reactions

1.1 Mole Concept and Molar Mass

• Mole Concept: $n=\frac{m}{M}$
• • Where:
  • • $n$ = number of moles
    • $m$ = mass of the substance (in grams)
    • $M$ = molar mass of the substance (in g/mol)
  • Explanation: The mole concept is used to count entities at the atomic scale by relating the amount of substance to its mass.
• Avogadro's Law: $V\propto n$ or $V=kn$
• • Where:
  • • $V$ = volume of gas
    • $n$ = number of moles of gas
    • $k$ = proportionality constant
  • Explanation: Avogadro's law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles.

1.2 Empirical and Molecular Formula

• Empirical Formula:
• • The simplest ratio of atoms in a compound. $\text{Empirical formula}=\text{Simplest ratio of moles of elements}$
• Molecular Formula: $\text{Molecular Formula}=\text{Empirical Formula}\times n$
• • Where:
  • • $n=\frac{\text{Molar Mass}}{\text{Empirical Formula Mass}}$

1.3 Balancing Chemical Equations

• Law of Conservation of Mass:
• • Total mass of reactants = Total mass of products.
• Balancing Equations:
• • Method of Inspection:
  • • Adjust coefficients to balance the number of atoms of each element on both sides of the equation.

Common Mistake:

Forgetting to balance all elements, including oxygen and hydrogen, often leads to incorrect stoichiometric calculations.

2. Thermodynamics

2.1 First Law of Thermodynamics

• Mathematical Form: $\Delta U=q+w$
• • Where:
  • • $\Delta U$ = change in internal energy
    • $q$ = heat added to the system
    • $w$ = work done on the system
  • Explanation: The first law is a statement of the conservation of energy, indicating that energy can neither be created nor destroyed.

2.2 Enthalpy ($\Delta H$)

• Relation with Internal Energy: $\Delta H=\Delta U+P\Delta V$Where:
• • • $\Delta H$ = change in enthalpy
    • $P$ = pressure
    • $\Delta V$ = change in volume
  • Explanation: Enthalpy change represents the heat absorbed or released under constant pressure conditions.

2.3 Hess's Law

• Mathematical Form: $\Delta H_{\text{reaction}}=\Sigma \Delta H_{\text{products}}-\Sigma \Delta H_{\text{reactants}}$
• • Explanation: The total enthalpy change of a reaction is the same, regardless of the number of steps in which the reaction is carried out.

NEET Problem-Solving Strategy:

Apply Hess's law by breaking down complex reactions into simpler steps with known enthalpy changes.

3. Chemical Kinetics

3.1 Rate of Reaction

• Average Rate: $\text{Rate}=\frac{-\Delta [\text{Reactant}]}{\Delta t}=\frac{\Delta [\text{Product}]}{\Delta t}$
• • Explanation: The rate of a reaction is the change in concentration of a reactant or product per unit time.

3.2 Arrhenius Equation

• Mathematical Form: $k=A{e}^{-\frac{E_a}{RT}}$
• • Where:
  • • $k$ = rate constant
    • $A$ = frequency factor
    • $E_a$ = activation energy
    • $R$ = universal gas constant
    • $T$ = temperature in Kelvin
  • Explanation: The Arrhenius equation shows the dependency of the reaction rate constant on temperature.

4. Equilibrium

4.1 Equilibrium Constant ($K_c$ and $K_p$)

• Concentration-Based Constant: $K_c=\frac{[\text{Products}]}{[\text{Reactants}]}$
• • Explanation: $K_c$ is the ratio of the product of the concentrations of the products to that of the reactants, each raised to their respective stoichiometric coefficients.
• Pressure-Based Constant: $K_p=K_c(RT{)}^{\Delta n}$
• • Where:
  • • $\Delta n$ = difference in the number of moles of gaseous products and reactants.

4.2 Le Chatelier's Principle

• Principle:
• • If a system at equilibrium is disturbed, the system shifts in the direction that minimizes the disturbance.

Quick Recap:

• Mole Concept: $n=\frac{m}{M}$
• First Law of Thermodynamics: $\Delta U=q+w$
• Rate of Reaction: $\text{Rate}=\frac{\Delta [\text{Product}]}{\Delta t}$
• Equilibrium Constant: $K_c=\frac{[\text{Products}]}{[\text{Reactants}]}$

Practice Questions:

1. Calculate the number of moles in 10 grams of $H_{2}O$.
2. Use Hess's Law to find the enthalpy change for a given reaction sequence.
3. Determine the rate constant using the Arrhenius equation at a specified temperature.
4. For a reaction at equilibrium, predict the shift in equilibrium when pressure is increased.

Common Mistake:

Confusing the units in thermodynamic calculations, especially between energy (Joules) and enthalpy (kJ).

This summary provides a concise collection of essential formulae and principles from the chapter "Elements and Periodicity in Properties" with brief explanations, examples, and strategies to avoid common mistakes, structured to aid NEET aspirants in their preparation.