Fundamental Concepts in Physics and Chemistry

Posted on Mar 9, 2025 in Chemistry

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Physics

Physics: Part of the science of physical phenomena.

  • Phenomenon: Any event under study.
  • Physical phenomena: A process that does not alter the nature of the substances involved.

Chemistry

Chemistry: Part of the science of chemical phenomena.

  • Chemical phenomena: A process that changes the nature of the substances involved.

The Scientific Method

Steps:

  1. Observation: Focusing on natural events to reproduce them in a laboratory setting.
  2. Experimentation: Repeating the phenomenon under study in the laboratory, modifying parameters to observe their influence.
  3. Hypothesis Formulation: Proposing explanations for the phenomena, which should be tested with further experiments.
  4. Development of Laws: If new experiments confirm the hypotheses, they become laws; otherwise, they are modified for further study.
  • Measurement: Comparing a magnitude with a standard unit.
  • Magnitude: Any measurable attribute.

Types of Magnitudes

  1. Scalar Magnitude: Defined by a number and a unit.
  2. Vector Magnitude: Requires a magnitude, direction, and point of application.
  3. Fundamental Magnitude: Determined by a system of units.
  4. Derived Magnitude: Obtained by applying mathematical expressions to fundamental values.

Giorgi International System (MKS)

  • Length: Meter (m)
  • Mass: Kilogram (kg)
  • Time: Second (s)

CGS System

  • Length: Centimeter (cm)
  • Mass: Gram (g)
  • Time: Second (s)

Technical System

  • Length: Meter (m)
  • Force: Kilopond (Kp)
  • Time: Second (s)

Kilogram-force (Kp): The force with which the Earth attracts a 1 kg mass placed in Ecuador.

Theory of Errors

Exact measurement is never possible, but an approximate measure can be obtained.

  • Absolute Error: The difference between the exact value and the measured value.
  • Relative Error: The ratio of the absolute error to the measured value.
  • Systematic Error: Error caused by the measuring instrument.
  • Accuracy: The smallest extent that can be measured with an instrument.
  • Accidental Error: Error made by the person taking the measurement.
  • Parallax Error: Error caused by the observer’s position.
  • Error On: Indicates the quality of the measurement; the lower the relative error, the better the measurement.

Weight Laws of Chemistry

  1. Law of Conservation of Mass: In any chemical process, mass is conserved.
  2. Law of Constant Proportions: In any chemical process, the relationship between the masses involved is constant.
  3. Law of Multiple Proportions: If two substances react in different chemical processes to give different compounds, the relationship between the mass of one of them reacting with a fixed amount of the other is a ratio of whole, simple numbers.

Laws of Volumetric Chemistry

  1. Law of Combining Volumes: In any chemical process carried out in the gas phase, keeping the pressure and temperature conditions constant, the relationship between the volumes of the substances involved is a ratio of whole, simple numbers.

Avogadro’s Hypothesis

Equal volumes of different gases at the same temperature and pressure contain the same number of molecules.

Molecule

A grouping of atoms (same or different) that is the smallest unit preserving the physical and chemical properties of a compound or element.

Molar Volume

One mole of any substance occupies 22.4 liters when measured under standard conditions (pressure = 1 atmosphere, temperature = 0°C).

Md: Amount of substance equal to its molecular weight in grams (old).

NA = 6.02 x 1023 molecules/mol (Avogadro’s Number)

Mole: A grouping of 6.02 x 1023 molecules of a substance.