Solved Questions on Physical and Chemical Changes
1. The reaction Mg + 2HCl → MgCl2 + H2 is an example of which type of reaction?
a) Combination reaction
b) Decomposition reaction
c) Displacement reaction
d) Precipitation Reaction
Answer: c) The reaction Mg + 2HCl → MgCl2 + H2 is an example of a displacement reaction. In this reaction, magnesium (Mg) displaces hydrogen (H) from hydrochloric acid (HCl) to form magnesium chloride (MgCl2) and hydrogen gas (H2). This type of reaction involves the replacement of one element by another in a compound.
2. Consider the following statements and choose the correct option:
Statement 1: The formation of dew on the grass is a physical change.
Statement 2: The burning of gasoline in a car engine is a chemical change.
a) Statement 1 is correct, but statement 2 is incorrect.
b) Statement 1 is incorrect, but statement 2 is correct.
c) Both statements are correct.
d) Both statements are incorrect.
Answer: c) Statement 1 is correct because the formation of dew on the grass involves a physical change where water vapour condenses into liquid water on the surface of the grass.
Statement 2 is correct. The burning of gasoline in a car engine is indeed a chemical change because it involves the combustion of gasoline, resulting in the formation of new substances.
3. In the following question, you will find an assertion and a reason. Select the appropriate option that applies.
Assertion: When iron nails are left in a moist environment, they rust over time.
Reasoning: Rusting is a chemical reaction that occurs when iron reacts with oxygen in the presence of water or moisture.
a) Both the assertion and reasoning are correct, and the reasoning correctly explains the assertion.
b) Both the assertion and reasoning are correct, but the reasoning does not correctly explain the assertion.
c) The assertion is correct, but the reasoning is incorrect.
d) The assertion is incorrect, but the reasoning is correct.
Answer: a) Both the assertion and reasoning are correct, and the reasoning correctly explains the assertion.
The assertion states that iron nails rust when exposed to a moist environment, which is correct. Rusting is a chemical reaction where iron reacts with oxygen in the presence of water or moisture, leading to the formation of iron oxide or rust. The reasoning correctly explains why iron nails rust in a moist environment.
4. Alicia and Maya conducted an experiment where they mixed baking soda (sodium bicarbonate) and vinegar (acetic acid) in a test tube. They observed the formation of bubbles and a fizzing sound. Which of the following statements accurately describes the change that occurred?
a) A physical change occurred, altering the physical properties of the substances.
b) A chemical change occurred, resulting in the formation of a new substance.
c) The experiment did not involve any change.
d) The change observed was due to a change in temperature.
Answer: b) A chemical change occurred, resulting in the formation of a new substance. When baking soda (sodium bicarbonate) and vinegar (acetic acid) are mixed, a chemical reaction takes place, leading to the formation of carbon dioxide gas. The bubbles and fizzing sound observed indicate the release of this gas, indicating a chemical change.
5. Which of the following statements accurately describes the difference between exothermic and endothermic reactions?
a) Exothermic reactions absorb heat from the surroundings, while endothermic reactions release heat to the surroundings.
b) Exothermic reactions occur at high temperatures, while endothermic reactions occur at low temperatures.
c) Exothermic reactions involve the production of gas, while endothermic reactions involve the absorption of gas.
d) Exothermic reactions release heat to the surroundings, while endothermic reactions absorb heat from the surroundings.
Answer: d) In exothermic reactions, energy in the form of heat is released to the surroundings, resulting in an increase in temperature. On the other hand, endothermic reactions absorb heat from the surroundings, causing a decrease in temperature.
FAQs
1. What are physical and chemical changes?
Physical change are changes to a substance's appearance or shape that do not affect its chemical material. Chemical changes, on the other hand, cause the production of new compounds with varying chemical characteristics.
2. How can we distinguish between physical and chemical changes?
Physical changes are reversible and do not result in the creation of new substances. Examples include state transitions (solid to liquid to gas), changes in form or size, and dissolution. However, chemical changes are unreversible and result in the development of new substances with distinct features. Examples are burning, rusting, and cooking.
3. What are some examples of physical and chemical changes?
Examples of physical changes include melting ice into water, freezing water into ice, crushing a can, tearing paper, dissolving salt in water, and cutting a piece of wood.
Examples of chemical changes include burning wood to produce ash and smoke, rusting of iron, cooking an egg, baking bread, fermenting grapes to make wine, and digesting food in the stomach.
4. Can physical and chemical changes be reversed?
Physical changes can often be reversed by applying the right conditions (such as altering temperature or pressure), however, chemical changes are usually irreversible.
5. How do physical and chemical changes occur?
Physical changes occur when the arrangement of molecules in a substance changes but the chemical content stays constant. Chemical changes occur when chemical bonds break and new bonds form, resulting in the production of various compounds.
