La Martiniere Girls' College Class VII Chemistry Chapter 5 PDF

Name: ___________________________________Date:__________________ Section: _____________ Roll No._______________ La Martiniere Girls’ College Class VII Chemistry...

Name: ___________________________________Date:__________________ Section: _____________ Roll No._______________ La Martiniere Girls’ College Class VII Chemistry Chapter 5 PHYSICAL AND CHEMICAL CHANGES PHYSICAL CHANGE: A physical change is a temporary, reversible change in which no new substance is formed and the composition of the original substance is not altered. Pour melted chocolate on ice cream.It still tastes the same because the particles have not changed; it just hardened (changed state) because the ice cream was cool. NATURE OF CHANGE: Temporary and reversible. FORMATION OF PRODUCTS: No new substances are formed. ENERGY CHANGE: Generally, energy is neither absorbed nor evolved during the change. Examples: Dissolving of sugar in water Melting of ice, butter or wax Boiling of water Sublimation Addition of salt to water CHEMICAL CHANGE A chemical change is a permanent, irreversible change in which a new substance is formed having different composition and properties. During rainy season, the iron gates are directly exposed to the rain water and air, which causes rusting. Rusting is a continuous process that corrodes the metal and makes it less durable, and it occurs in the presence of air and water. Hence, the iron gates are coated with paint to prevent rusting and corrosion. NATURE OF CHANGE: Permanent and irreversible FORMATION OF PRODUCTS: New substances are formed. ENERGY CHANGE: Generally, energy is either absorbed or evolved during the change. Examples: Burning of magnesium, sulphur powder and paper Conversion of milk into curd Digestion of food Photosynthesis Respiration LMGC/CL 7/CHEMISTRY/Ch.No.5 Page 1 of 3 EXAMPLES PHYSICAL CHANGE CHEMICAL CHANGE 1. Casually mixing iron powder with Reacting iron with sulphur to produce sulphur powder is a physical change. iron sulphide is a chemical change. 2. Cutting a piece of paper with Burning a piece of paper is a chemical scissors is a physical change. change. 3. Rolling of chapati is a physical Baking of chapati is a chemical change. change. 4. Cutting a piece of nylon fabric with Burning a piece of nylon is a chemical scissors is a physical change. change. How to Tell Chemical & Physical Changes Apart In physical change the appearance or form of the matter changes but the composition in the substance does not change. Various signs of a chemical change are: Change in colour Change in temperature Change in odour Formation of a gas Formation of a precipitate Formation of bubbles Light is being produced EXERCISES 1. Define a. Physical change b. Chemical change 2. Give two indications that a chemical change has occurred. 3. What is the difference between a physical and a chemical change? 4. Which of the following is not a chemical change characteristic? a. Change in colour b. Change in state c. Production of sound d. Change in smell 5. Your friend decides to toast a piece of bread, but leaves it in the toaster too long. The bread is black and the kitchen if full of smoke. Is it physical or chemical change? LMGC/CL 7/CHEMISTRY/Ch.No.5 Page 2 of 3  La Martiniere Girls’ College Class VII Chemistry Chapter 5 PHYSICAL AND CHEMICAL CHANGES Classify the following as physical change or chemical change: LMGC/CL 7/CHEMISTRY/Ch.No.5 Page 3 of 3