Understanding Physics and Chemistry: Basic Principles

Posted on Mar 3, 2025 in Chemistry

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Physics and Chemistry: Basic Concepts

Physics

Part of the science of physical phenomena.

  • Phenomenon: Any event under study.
  • Physical Phenomena: Processes that do not alter the nature of the substances involved.

Chemistry

Part of the science of chemical phenomena.

  • Chemical Phenomena: Processes that change the nature of the substances involved.

The Scientific Method

The scientific method consists of the following steps:

  1. Observation: Noting fixed natural events in order to reproduce them in the laboratory.
  2. Experimentation: Repeating the phenomenon studied in the laboratory, modifying certain parameters to observe their possible influence.
  3. Hypothesis Formulation: Proposing explanations of the phenomena, which should be demonstrated through new experiments.
  4. Development of Laws: Once new experiments confirm the hypotheses, they are transformed into laws. If not, they are modified for further study.
  • Measurement: Comparing a magnitude with a standard unit.
  • Magnitude: Any attribute that can be measured.

Types of Magnitudes

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

Measurement Systems

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

  • An 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: The error introduced by the measuring instrument.
  • Accuracy: The smallest extent that can be measured with an instrument.
  • Accidental Error: The error made by the person performing the measurement.
  • Parallax Error: An error in observation due to the observer’s position.
  • Error On: Indicates the quality of the measurement; the lower the relative error, the better the measurement.

Laws of Chemistry

Weight Laws

  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 masses of one of them reacting with a fixed amount of the other is a ratio of whole, simple numbers.

Volumetric Laws

  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 the 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).

Definitions

  • Md: Amount of substance equal to its molecular weight in grams (old definition).
  • Avogadro’s Number (NA): 6.022 x 1023 molecules/mol.
  • Mole: A grouping of 6.022 x 1023 molecules of a substance.