التغيرات الكيميائية والفيزيائية

Introduction to Chemical and Physical Changes

• Chemical changes involve a transformation of substances into new substances with different properties.
• Physical changes alter the state or form of a substance without changing its chemical composition.

Identifying Physical Changes

• Changes in state (e.g., melting, freezing, vaporization, condensation, sublimation):
  • These changes involve a rearrangement of molecules but do not create new substances.
  • Example: Ice melting into water.
• Changes in shape or size (e.g., cutting, bending, crushing):
  • These changes don't alter the chemical makeup of the substance.
  • Example: Crushing a piece of chalk.
• Dissolving:
  • When a substance dissolves in a solvent, its particles disperse throughout the solvent.
  • Example: Sugar dissolving in water.
• Changes in physical properties (e.g., density, color, texture, odor):
  • These changes only affect the physical appearance and do not change the chemical identity of the substance.
  • Example: Iron rusting. Although the color changes, the chemical formula has changed creating a new substance. Important to note Physical changes can change a substance's appearance, but do not alter its chemical makeup.
• Filtration, distillation, and chromatography are common physical separation techniques.

Identifying Chemical Changes

• Formation of a precipitate (a solid formed from a solution):
  • When two solutions are mixed, a solid may form and settle out.
  • Example: Mixing silver nitrate and sodium chloride solutions forming silver chloride precipitate.
• Evolution of gas:
  • The production of bubbles or gases as a result of reaction.
  • Example: Baking soda and vinegar reacting.
• Color change:
  • A change in colour often accompanied by a change in the chemical makeup of the substance.
  • Example: Iron rusting.
• Change in temperature:
  • A change in temperature can indicate a chemical reaction, often accompanied by either heat loss or heat production.
  • Example: Combustion (fire) releases heat energy.
• Formation of a new substance with different properties:
  • Chemical reactions create substances such as compounds or elements with new properties, different from that of the original substances.
  • Example: Burning wood; the wood (cellulose) changes to new substances like ash and other byproducts/gases.

Examples of Physical Changes

• Ice melting (water to liquid)
• Water boiling (liquid to gaseous state)
• Bending a wire
• Cutting wood
• Dissolving salt in water

Examples of Chemical Changes

• Burning wood
• Rusting of iron
• Baking a cake (new substances are formed)
• Digesting food in the stomach (enzymes alter food molecules to create new ones)
• Formation of a cloud from water vapor
• Souring milk
• Fireworks exploding
• Cooking an egg. The albumen in the egg changes structure.
• Taking medication. The medicine changes how the body functions.
• Photosynthesis: This is a chemical process. Plants use sunlight, carbon dioxide, and water to create glucose and oxygen. Glucose and oxygen are new substances formed from the initial reactants.

Distinguishing Between Physical and Chemical Changes

• Chemical changes result in new substances with new properties.
• Physical changes do not result in new substances.

Importance of Understanding Chemical and Physical Changes

• Identifying chemical and physical changes is essential in various fields of science, engineering, and daily life.
• Understanding these changes helps predict the outcome of different procedures and processes.
• Everyday activities (cooking, cleaning, etc.) frequently involve both kinds of changes. You will also find these changes at play in processes at work like manufacturing and construction, and even on a larger scale like environmental effects.

Key Differences Summarized

يتناول هذا الاختبار مفهوم التغيرات الكيميائية والفيزيائية. ستتعرف على كيفية تمييز التغيرات الفيزيائية وتفاصيل التغيرات في الحالة والشكل والحجم. يمكن أن يساعدك هذا الاختبار في فهم كيفية تأثير هذه التغيرات على المواد.