Chemical Reactions-02 -

TOTAL NUMBER OF QUESTIONS:50

Exam

Q1. What helps us determine that a chemical reaction has taken place?

A. Only a change in state

B. Only a change in colour

C. Change in state, colour, temperature, or evolution of gas

D. Only evolution of gas

Q2. What is the chemical change described when a magnesium ribbon is burnt in oxygen?

A. Magnesium oxide is converted to magnesium.

B. Magnesium gets converted to magnesium oxide.

C. Oxygen gets converted to magnesium.

D. No new substance is formed.

Q3. What is the simplest way to write a description of a chemical reaction?

A. As a paragraph

B. As a word-equation

C. As a detailed essay

D. As a single symbol

Q4. In the word-equation: Magnesium + Oxygen → Magnesium oxide, what are ‘Magnesium’ and ‘Oxygen’ called?

A. Products

B. Reactants

C. Results

D. Mixtures

Q5. In a word-equation, what does the arrow (→) show?

A. The direction of the reaction

B. That reactants and products are equal

C. A plus sign

D. The temperature of the reaction

Q6. In a word-equation, where are the reactants written?

A. On the Right Hand Side (RHS) with a plus sign

B. On the Left Hand Side (LHS) with a plus sign

C. Above the arrow

D. Below the arrow

Q7. In a word-equation, where are the products written?

A. On the Left Hand Side (LHS)

B. On the Right Hand Side (RHS) with a plus sign

C. On both sides

D. Nowhere

Q8. What is a more concise way to represent a chemical equation than a word-equation?

A. Using longer descriptions

B. Using chemical formulae instead of words

C. Using pictures only

D. Using only numbers

Q9. What is a skeletal chemical equation?

A. An equation with the same number of atoms on both sides

B. An unbalanced equation where mass is not conserved

C. An equation written only in words

D. An equation with state symbols

Q10. Which law states that mass can neither be created nor destroyed in a chemical reaction?

A. Law of constant proportions

B. Law of conservation of mass

C. Law of multiple proportions

D. Newton’s law

Q11. According to the law of conservation of mass, what remains the same before and after a chemical reaction?

A. The number of molecules of each compound

B. The physical state of each element

C. The number of atoms of each element

D. The colour of the substances

Q12. Why do we need to balance a chemical equation?

A. To make it look longer

B. To obey the law of conservation of mass

C. To change the reactants

D. To include the temperature

Q13. In the balanced equation Zn + H₂SO₄ → ZnSO₄ + H₂, how many hydrogen atoms are on each side?

A. 1

B. 2

C. 3

D. 4

Q14. What is the first step suggested for balancing a chemical equation?

A. Change the formulae of the compounds.

B. Draw boxes around each formula.

C. Start balancing the oxygen atoms first.

D. Write the physical states.

Q15. When starting to balance an equation, it is often convenient to start with the compound that has what?

A. The minimum number of atoms

B. The colour change

C. The maximum number of atoms

D. The gaseous state

Q16. What does the symbol (s) represent in a chemical equation?

A. Solution

B. Solid state

C. Liquid state

D. Gas state

Q17. What does the symbol (l) represent in a chemical equation?

A. Light

B. Liquid state

C. Large quantity

D. Less than

Q18. What does the symbol (g) represent in a chemical equation?

A. Gravitational force

B. Green colour

C. Gas state

D. Grams

Q19. What does the symbol (aq) represent in a chemical equation?

A. A quantity

B. Aquatic

C. Aqueous (solution in water)

D. Air quality

Q20. In the equation 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g), what does (g) with H₂O indicate?

A. Water is ice.

B. Water is a liquid.

C. Water is in the form of steam.

D. Water is dissolved.

Q21. Are physical states always included in a chemical equation?

A. Yes, always.

B. No, they are always excluded.

C. Usually they are not included unless necessary to specify them.

D. Only for solids.

Q22. Where are reaction conditions like temperature or catalyst indicated in a chemical equation?

A. Before the reactants

B. After the products

C. Above and/or below the arrow in the equation

D. Only in the word-equation

Q23. In the reaction for the formation of methanol, what condition is written below the arrow?

A. Sunlight

B. 340 atm

C. Chlorophyll

D. (s)

Q24. In the photosynthesis equation, what are the conditions mentioned above the arrow?

A. 340 atm

B. Sunlight / Chlorophyll

C. High temperature

D. (aq)

Q25. What is the product when hydrogen reacts with chlorine according to the word-equation?

A. Hydrogen chloride

B. Hydrogen peroxide

C. Chlorine water

D. Hydrogen gas

Q26. In a chemical reaction, do atoms of one element change into atoms of another element?

A. Yes, always.

B. No, they never do.

C. Sometimes they do.

D. Only in decomposition reactions.

Q27. What do chemical reactions actually involve at the atomic level?

A. Disappearance of atoms

B. Creation of new atoms

C. Breaking and making of bonds between atoms

D. Only mixing of atoms

Q28. What is the new substance formed in the reaction of zinc and sulphuric acid?

A. Zinc and hydrogen

B. Zinc sulphate and hydrogen

C. Sulphuric acid only

D. Zinc oxide

Q29. If the number of atoms of each element is the same on both sides of an equation, what is it called?

A. A skeletal equation

B. A word-equation

C. An unbalanced equation

D. A balanced chemical equation

Q30. What should you NOT change while balancing a chemical equation?

A. The coefficients in front of formulae

B. Anything inside the boxes drawn around formulae

C. The order of reactants

D. The physical states

Q31. What does the ‘+’ sign between reactants in a word-equation represent?

A. They are multiplied.

B. They are added together.

C. They are in different states.

D. They are products.

Q32. From the atom count for Fe + H₂O → Fe₃O₄ + H₂, how many iron atoms are on the product side?

A. 1

B. 3

C. 4

D. 2

Q33. From the atom count for Fe + H₂O → Fe₃O₄ + H₂, how many oxygen atoms are on the reactant side?

A. 1

B. 4

C. 2

D. 3

Q34. What information does a balanced chemical equation without state symbols NOT give?

A. The identities of reactants and products

B. The physical states of reactants and products

C. The ratio of molecules/atoms

D. The direction of the reaction

Q35. To make a chemical equation more informative, what can be added along with the chemical formulae?

A. The price of chemicals

B. The physical states of reactants and products

C. The name of the scientist

D. The date of the reaction

Q36. In the final balanced form of the iron and steam reaction, what is the coefficient of H₂?

A. 2

B. 3

C. 4

D. 1

Q37. What does a chemical equation represent?

A. Only the speed of a reaction

B. The identities and proportions of reactants and products

C. Only the colour changes

D. Only the gases involved

Q38. What is the first step in going from a word description to a chemical equation?

A. Balance the atoms.

B. Write the word-equation.

C. Add state symbols.

D. Write the skeletal formula equation.

Q39. What must be true for a chemical equation to obey the law of conservation of mass?

A. It must be a word-equation.

B. It must be balanced.

C. It must have state symbols.

D. It must have an arrow.

Q40. In the photosynthesis equation 6CO₂(aq) + 6H₂O → C₆H₁₂O₆(aq) + 6O₂(g), what is the physical state of glucose?

A. (s)

B. (g)

C. (l)

D. (aq)

Q41. What is the primary purpose of the arrow in a chemical equation?

A. To separate reactants from products

B. To show the reaction yields products from reactants

C. To indicate heat is applied

D. To show the reaction is reversible

Q42. According to the text, what does NOT happen to atoms during a chemical reaction?

A. They form new bonds.

B. They do not disappear from the mixture.

C. They do not appear from elsewhere.

D. They change into atoms of another element.

Q43. What is the reactant in the burning of magnesium?

A. Magnesium oxide only

B. Oxygen only

C. Magnesium and Oxygen

D. Heat

Q44. In the skeleton equation Mg + O₂ → MgO, why is it unbalanced?

A. The formula of MgO is wrong.

B. The number of oxygen atoms is not equal on both sides.

C. The plus sign is missing.

D. The arrow is missing.

Q45. Which step in balancing involves listing the number of atoms of each element?

A. Step I

B. Step II

C. Step III

D. Step VII

Q46. What is the main characteristic of a skeletal chemical equation?

A. It is balanced.

B. It has state symbols.

C. It is unbalanced.

D. It has reaction conditions.

Q47. What is the correct word-equation for the reaction of sodium and water?

A. Sodium + Water → Sodium oxide + Hydrogen

B. Sodium + Water → Sodium hydroxide + Hydrogen

C. Sodium hydroxide → Sodium + Water

D. Sodium + Hydrogen → Sodium hydroxide

Q48. What are the products in the reaction: Barium chloride + Aluminium sulphate → ?

A. Barium sulphate + Aluminium chloride

B. Barium aluminium + Chloride sulphate

C. Barium chloride + Aluminium sulphate

D. Barium oxide + Aluminium oxide

Q49. In the final balanced equation, what is the physical state of the product iron oxide (Fe₃O₄)?

A. (g)

B. (aq)

C. (l)

D. (s)

Q50. Based on the text, what is the ultimate goal of writing and balancing a chemical equation?

A. To make it look complex

B. To represent a chemical change accurately and informatively

C. To use as many symbols as possible

D. To hide the reaction details