Understanding Chemical Equations: Balancing, Types, and Calculations

Posted on Mar 9, 2025 in Geology

Understanding Chemical Equations

The Matmata method of equalization in chemical equations involves ensuring that the number of atoms of each element is equal on both sides of the equation.

Methods for Balancing Chemical Equations

The method involves testing coefficients for the elements involved. This begins by adjusting coefficients for elements involved in the compounds.

Types of Chemical Reactions

  • Decomposition or Chemical Analysis: AB → A + B
  • Synthesis: A + B → AB
  • Displacement or Replacement: AB + C → C + B
  • Double Substitution: AB + CD → AC + BD
  • Reversible Reaction: Products ⇄ Reactants
  • Chained Reactions: A + B → C + D — D + E → F + G

Acids and Bases

  • Acids dissociate in solution, releasing H+ ions: H+ + A-
  • Bases dissociate in solution, releasing OH- ions: B+ + OH-

Strength of Acids and Bases

Strong acids and bases dissociate completely in solution, while weak acids and bases dissociate partially.

pH Scale

  • Acidic: pH < 7, [H+] > 10-7 M
  • Neutral: pH = 7, [H+] = 10-7 M
  • Basic: 7 < pH < 14, [H+] < 10-7 M

Neutralization

Neutralization is the reaction between an acid and a base to produce a salt and water: Acid + Base → Salt + Water

Combustion Reactions

In a combustion reaction, any organic substance combusts to produce carbon dioxide and water: CxHy + O2 → xCO2 + y/2 H2O

Exothermic and Endothermic Reactions

  • Exothermic Reaction: A chemical reaction that releases energy.
  • Endothermic Reaction: A chemical reaction that absorbs energy.

Thermochemical Equations

A thermochemical equation includes the chemical equation and the energy absorbed or released during the reaction, the state of reactants and products, and the conditions of pressure and temperature under which the reaction is performed. Standard conditions: P = 1 atm, T = 25°C.

Internal Energy and Enthalpy Variations

  • Internal Energy Variation (ΔU): Heat measured at constant volume, qv.
  • Enthalpy Variation (ΔH): Heat measured at constant pressure, qp.

The enthalpy of elements in their standard and stable form is considered zero. The enthalpy of a reaction can be expressed using the enthalpies of formation of reactants and products, or using bond enthalpies:

ΔHreaction = ΔHproducts – ΔHreactants

ΔHreaction = ΔHbonds broken – ΔHbonds formed

Stoichiometric Calculations

In stoichiometric calculations, amounts are always converted to moles. Conversion factors are used.

Limiting Reactant

The limiting reactant is the reactant present in a smaller amount than required by the stoichiometric proportion. It is completely consumed during the reaction.

Excess Reactant

The excess reactant is the reactant present in an amount greater than required by the stoichiometric proportion.

Yield

Yield is the quantity of product obtained compared to the theoretical quantity expected.

Scientific Method and Measurement

Hypothesis

A hypothesis is an explanation for a problem that requires experimental verification. A hypothesis shows the quantitative relationship between two or more variables.

Theory

A theory is a set of coherent and consistent laws.

Physical Scale

A physical scale is a property of a process that can be measured.

Scalar Magnitude

A scalar magnitude is defined by a number and a corresponding unit.

Vectorial Magnitude

A vectorial magnitude is defined by a number, a unit, a direction, and a sense of application.

Fundamental Magnitude

A fundamental magnitude is a magnitude that is not defined in terms of other magnitudes.

Derived Magnitude

A derived magnitude is a magnitude defined based on fundamental magnitudes.

Measurement

Measurement is comparing a quantity with another quantity of the same magnitude.

Fidelity

An instrument is faithful if, when used to make a set of measurements of the same magnitude under the same conditions, the values are close together.

Sensitivity

Sensitivity is the minimum change in a quantity that an instrument can detect.

Precision

An instrument is precise if, when used to make multiple measurements of the same magnitude under the same conditions, each value is close to the true value.

Precision in Measurements

Measurements are precise if the values do not vary much.

Accuracy in Measurements

A measurement is accurate if the relative error is very small.