chemical change

Examples of chemical 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.
  • Many physical changes are reversible (such as heating and cooling), whereas chemical changes are often irreversible or only reversible with an additional chemical change.
  • Chemical changes are also known as chemical reactions.

• Changes in Temperature

  • Changes in temperature shift the equilibrium state of chemical reactions; these changes can be predicted using Le Chatelier's Principle.
  • Changes in temperature can affect the equilibrium state of a reversible chemical reaction.
  • Le Chatelier's Principle states that when changes are made to a reversible chemical reaction in equilibrium, the system will compensate for that change with a predictable, opposing shift.
  • This law can be applied to changes in pressure, volume, concentration, and temperature.
  • Evaluate the effect of temperature on the equilibrium state of a chemical reaction

• Energy Changes in Chemical Reactions

  • Due to the absorption of energy when chemical bonds are broken, and the release of energy when chemical bonds are formed, chemical reactions almost always involve a change in energy between products and reactants.
  • By the Law of Conservation of Energy, however, we know that the total energy of a system must remain unchanged, and that oftentimes a chemical reaction will absorb or release energy in the form of heat, light, or both.
  • The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants.
  • This stored chemical energy, or heat content, of the system is known as its enthalpy.
  • Describe the types of energy changes that can occur in chemical reactions

• 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.
  • A chemical property, meanwhile, is any of a material's properties that becomes evident during a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity.
  • Physical properties are properties that can be measured or observed without changing the chemical nature of the substance.
  • Remember, the definition of a chemical property is that measuring that property must lead to a change in the substance's chemical structure.
  • Hydrolysis and oxidation are two such reactions and are both chemical changes.

• Change in Enthalpy

  • Enthalpy changes are associated with chemical processes, and are important in understanding how the reaction has changed a chemical system.
  • Any time a thermodynamic system undergoes a transformation or a chemical reaction, there is an energy (enthalpy) change associated with the process.
  • Any chemical reaction can be characterized by a change in enthalpy, denoted as: $\Delta H = \Delta H_{final} - \Delta H_{initial}$
  • By determining the value of the change of enthalpy, you can determine whether the reaction is endothermic (positive change) or exothermic (negative change).
  • This lesson introduces Enthalpy and the energy of chemical bonding.

• Chemical Kinetics and Chemical Equilibrium

  • Chemical kinetics is the study of how quickly a chemical reaction occurs and what factors affect its rate.
  • The study of these factors and rates is known as chemical kinetics.
  • The interval required for a chemical change or reaction to occur is called the reaction time.
  • This rate can be expressed as the ratio of the change in the concentration of a reactant (or product) to the change in time.
  • Actually measuring the rates of change in the reactants and products is difficult.

• Introduction to Chemical Reactivity

  • Chemical Reaction: A transformation resulting in a change of composition, constitution and/or configuration of a compound (referred to as the reactant or substrate).
  • Reactant or Substrate: The organic compound undergoing change in a chemical reaction.
  • Reagent: A common partner of the reactant in many chemical reactions.
  • Catalysts are substances that accelerate the rate ( velocity ) of a chemical reaction without themselves being consumed or appearing as part of the reaction product.
  • Catalysts do not change equilibria positions.

• Balancing Chemical Equations

  • A chemical equation is an expression of the net composition change associated with a chemical reaction.
  • In addition, they always adhere to the law of conservation of mass, which holds that matter can change form, but cannot be created or destroyed.
  • A properly balanced chemical equation shows this.
  • Never attempt to balance a reaction by changing the subscripts on a molecule.
  • The subscripts indicate a very specific molecule; changing the subscripts would indicate a new molecule (not the desired product).

• Chemical Manufacturing

  • Chemical manufacturing is a subset of chemical industry involved in the conversion of raw materials into value-added products.
  • Basic chemicals, or "commodity chemicals" are a broad chemical category including polymers, bulk petrochemicals and intermediates, other derivatives and basic industrials, inorganic chemicals, and fertilizers.
  • Specialty Chemicals are sometimes referred to as "fine chemicals. "
  • The European Community remains the largest producer area followed by the USA and Japan.The traditional dominance of chemical production by the Triad countries is being challenged by changes in feedstock availability and price, labour cost, energy cost, differential rates of economic growth and environmental pressures.
  • Instrumental in the changing structure of the global chemical industry has been the growth in China, India, Korea, the Middle East, South East Asia, Nigeria, and Brazil.

• Substances and Mixtures

  • In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties.
  • Chemical substances can be solids, liquids, gases, or plasma.
  • Changes in temperature or pressure can cause substances to shift between the different phases of matter.
  • A pure chemical compound is a chemical substance that is composed of a particular set of molecules or ions that are chemically bonded.
  • Two or more elements combined into one substance through a chemical reaction, such as water, form a chemical compound.