physical change

Examples of physical change in the following topics:

• Physical and Chemical Changes to Matter

  • There are two types of change in matter: physical change and chemical change.
  • There are two types of change in matter: physical change and chemical change.
  • As the names suggest, a physical change affects a substance's physical properties, and a chemical change affects its chemical properties.
  • They are also physical changes because they do not change the nature of the substance.
  • The formation of gas bubbles is often the result of a chemical change (except in the case of boiling, which is a physical change).

• Physical and Chemical Properties of Matter

  • Both extensive and intensive properties are physical properties, which means they can be measured without changing the substance's chemical identity.
  • For example, the freezing point of a substance is a physical property: when water freezes, it's still water (H2O)—it's just in a different physical state.
  • Physical properties are properties that can be measured or observed without changing the chemical nature of the substance.
  • Some examples of physical properties are:
  • Hydrolysis and oxidation are two such reactions and are both chemical changes.

• Experimental Determination of Reaction Rates

  • There are two main ways to measure the concentrations of reactions: by measuring the changes in an observable physical property, or by taking samples of the reaction solution and measuring concentration directly.
  • Physical measurements can be performed on the system while it is reacting.
  • For example, if the total number of moles of gas changes during a gas reaction, the course of the reaction can be measured by monitoring the change in pressure at a constant volume.
  • Other physical measurements include optical methods, such as measuring the change in light polarization, the change in the refractive index of the solution, or quite commonly, the change in the color of the solution, and therefore the absorption spectrum.
  • Design experiments that use either chemical or physical properties to measure reaction rates

• Interference and Diffraction

  • Interference and diffraction are terms that describe a wave interacting with something that changes its amplitude, such as another wave.
  • In physics, interference is a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude.
  • In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.
  • It is just a question of usage, and there is no specific, important physical difference between them."
  • While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves where the wavelength is roughly similar to the dimensions of the diffracting objects.

• Bond Enthalpy

  • Bond enthalpy is defined as the enthalpy change when a covalent bond is cleaved by homolysis.
  • Enthalpy is a measure of the total heat energy content in a thermodynamic system, and it is practically used to describe energy transfer during chemical or physical processes in which the pressure remains constant.
  • Thus, the change in enthalpy, $\Delta H$, is a more useful quantity than its absolute value.
  • Generally, a positive change in enthalpy is required to break a bond, while a negative change in enthalpy is accompanied by the formation of a bond.
  • Describe the changes in enthalpy accompanying the breaking or formation of a bond

• Variation of Physical Properties Within a Group

  • The physical properties (notably, melting and boiling points) of the elements in a given group vary as you move down the table.
  • A physical property of a pure substance can be defined as anything that can be observed without the identity of the substance changing.
  • Physical properties include such things as:
  • This means the elements of a group often exhibit similar chemical reactivity, and there may be similarities in physical properties as well.
  • Describe the general trends of physical properties within a group on the periodic table.

• Three States of Matter

  • The three states of matter are the distinct physical forms that matter can take: solid, liquid, and gas.
  • The three states of matter are the three distinct physical forms that matter can take in most environments: solid, liquid, and gas.
  • Solids can only change shape under force, as when broken or cut.
  • This process of a liquid changing to a gas is called evaporation.
  • What does a phase change look like at the molecular level?

• Physical Properties of Carboxylic Acids

  • Again, changes in crystal packing and intermolecular forces are responsible.

• Variation of Physical Properties Across a Period

  • The physical properties of elements vary across a period, mostly as a function of bonding.
  • As you move across a period in the periodic table, the types of commonly encountered bonding interactions change.
  • Another physical property that varies across a period is the melting point of the corresponding halide.
  • The physical properties of the chlorides of elements in Groups 1 and 2 are very different compared to the chlorides of the elements in Groups 4, 5, and 6.
  • Describe the general variations in physical properties across a row of the periodic table.

• Microstates and Entropy

  • For any physically realizable macrostate, the quantity Ω is an unimaginably large number.
  • Even though it is beyond human comprehension to compare numbers that seem to verge on infinity, the thermal energy contained in actual physical systems manages to discover the largest of these quantities with no difficulty at all, quickly settling in to the most probable macrostate for a given set of conditions.
  • In terms of energy, when a solid becomes a liquid or a liquid a vapor, kinetic energy from the surroundings is changed to ‘potential energy‘ in the substance (phase change energy).
  • Phase-change energy increases the entropy of a substance or system because it is energy that must be spread out in the system from the surroundings so that the substance can exist as a liquid or vapor at a temperature above its melting or boiling point.