Hasooleilm LMS Hasooleilm LMS
Course Content
Unit 1: Plant System
Unit 2: Human Respiratory and Circulatory System
Unit 3: Immunity and Diseases
Unit 4: Structure of an Atom
Unit 5: Physical and Chemical Changes
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Physical Changes
Physical Changes
Chemical Changes
Chemical Changes
Impact of Burning on the Environment
Impact of Burning on the Environment
Rusting and Tarnishing of Metals
Rusting and Tarnishing of Metals
Difference Between Chemical and Physical Properties of Matter
Physical and Chemical Properties of Matter
Solution To Exercise
Unit 5: Physical and Chemical Changes – Full Chapter Quiz
Unit 6: Chemical Bonds
Unit 7: Solutions
Unit 8: Force and Motion
Unit 9: Waves and Energy
Unit 10: Heat and Temperature
Unit 11: Earth and Space
Unit 12: Technology in Everyday Life
New Oxford Secondary Science Book 7 (Terry Jennings)

Multiple Choice Questions

  1. d) Rusting
  2. a) Changing size
  3. b) Baking bread dough
  4. d) Exploding a firework
  5. d) Wax

Fill in the Blanks

  1. When a fuel burns, it releases heat energy.
  2. Rusting of steel is an example of a chemical change.
  3. Fuel reacts with oxygen gas when it burns.
  4. In a chemical change, atoms are rearranged to form molecules.
  5. When carbon burns, carbon dioxide gas is produced.

Short Questions

  1. One change that happens during a chemical change in baking a cake is the transformation of raw ingredients into a completely different substance with different properties, such as the conversion of cake batter into a solid, fluffy cake with a different taste and texture.
    1. Word equation for the breakdown of sodium hydrogen carbonate:Sodium hydrogen carbonate (baking powder) → Sodium carbonate + Carbon dioxide + Water
    2. Baking powder is added to the cake mixture to help the cake rise and become fluffy. The carbon dioxide gas produced during the breakdown of sodium hydrogen carbonate creates bubbles in the cake mixture, making the cake light and airy.
    3. To test for carbon dioxide gas, one can use the effervescence (bubbling) test. Collect the gas released during the reaction (e.g., by placing a container over the mixture), and then bubble the gas through limewater (calcium hydroxide solution). If the limewater turns cloudy or milky, it indicates the presence of carbon dioxide.

Scientific Facts

  • The only state of matter that is easily compressed is gas.
  • When particles are heated, they gain kinetic energy and move faster.
  • The two states of matter that flow easily are liquid and gas.
  • Two examples of chemical changes are burning wood and digesting food.
  • A hydrocarbon is a compound consisting entirely of hydrogen and carbon atoms.
  • A fuel is any substance that reacts with other substances to release energy as heat. Examples include gasoline and natural gas.

Long Answer Questions

i. Difference Between Physical and Chemical Change:

Physical Change: Physical changes are changes in which the substance’s identity remains the same even though its physical appearance or state may change. No new substances are formed during a physical change. Examples include melting ice (from solid to liquid) and evaporating water (from liquid to gas).
Chemical Change: Chemical changes are changes in which the substances involved are transformed into new substances with different properties. Chemical bonds are broken and new bonds are formed. Examples include burning wood (producing ash and smoke), digesting food (breaking down complex molecules into simpler ones), and rusting iron (forming iron oxide).

Equations for Combustion, Rusting, and Ammonia Formation

Combustion: Combustion is the reaction of a substance with oxygen to produce heat and light. The general equation for the combustion of a hydrocarbon (like methane, CH4) is: CH4 + 2O2 -> CO2 + 2H2O

Rusting: Rusting is the corrosion of iron in the presence of oxygen and moisture. The equation for rusting can be simplified as: 4Fe + 3O2 + 6H2O -> 4Fe(OH)3

Ammonia Formation: The formation of ammonia (NH3) can be represented by the equation: N2 + 3H2 -> 2NH3

Reversible Reactions: Reversible reactions are chemical reactions that can proceed in both the forward and reverse directions. In other words, the products of a reversible reaction can react together to form the original reactants.

Examples include the dissociation of water into hydrogen and oxygen (2H2O <-> 2H2 + O2) and the equilibrium reaction between carbon dioxide and water to form carbonic acid (CO2 + H2O <-> H2CO3

Changes Observed During a Chemical Reaction:

  • Change in color
  • Formation of a precipitate (solid)
  • Evolution of gas (bubbles)
  • Change in temperature (heat is absorbed or released)
  • Change in odor
  • Formation of a new substance with different properties

Think About It:

  • Compounds that contain carbon and hydrogen are called hydrocarbons.
    The gas produced when carbon burns in a good supply of oxygen is carbon dioxide (CO2).
  • Word equation for the burning of hydrogen in oxygen:
    2H2 + O2 -> 2H2O
    The reactants of the above reaction are hydrogen (H2) and oxygen (O2).
  • The products of the above reaction are water vapor (H2O). a) Methane (CH4) contains the elements carbon (C) and hydrogen (H). Octane (C8H18) also contains carbon and hydrogen.
  • Methane (CH4) contains the elements carbon (C) and hydrogen (H). Octane (C8H18) also contains carbon and hydrogen.
  • When methane is burnt, the two compounds formed are carbon dioxide (CO2) and water vapor (H2O).
  • The formulae for the two products formed when methane is burnt are CO2 and H2O.
  • Word equation for the burning of methane: CH4 + 2O2 -> CO2 + 2H2O
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