7th Grade Test Chemical Reactions

23. Identify the reaction type: KCl + AgNO₃ → KNO₃ + AgCl

• a) Synthesis
• b) Decomposition
• c) Single replacement
• d) Double replacement

24. The reaction rate is the __________ at which a chemical reaction occurs, measured by how fast __________ transform into __________.

• a) Speed; reactants; products
• b) Mass; atoms; ions
• c) Volume; moles; solutions
• d) Pressure; catalysts; inhibitors

25. The collision model states that for a reaction to occur, reactant particles must:

• a) Have enough energy and correct orientation
• b) Be at a low temperature
• c) Form a solid precipitate
• d) Absorb heat energy

26. In the equation 2H₂ + O₂ → 2H₂O, what do the coefficients indicate?

• a) The total number of molecules in the reaction
• b) The relative number of molecules of each substance in the reaction
• c) The atomic mass of the elements involved
• d) The number of electrons gained or lost

27. The law of conservation of mass states that:

• a) Mass can be created but not destroyed
• b) The total mass of reactants must equal the total mass of products
• c) Energy is always absorbed in a chemical reaction
• d) The total number of atoms changes after a reaction

28. What is the correct classification for this reaction? Fe + CuSO₄ → FeSO₄ + Cu

• a) Synthesis
• b) Decomposition
• c) Single replacement
• d) Double replacement

29. The molar mass of NaCl (sodium chloride) is approximately:

• a) 35.5 g/mol
• b) 58.5 g/mol
• c) 22.0 g/mol
• d) 100.5 g/mol

30. How many molecules are in one mole of a substance?

• a) 6.022 × 10²³
• b) 3.14 × 10²³
• c) 1.00 × 10³
• d) 9.81 × 10²²

31. How do you determine the molar mass of a compound?

• a) Add the atomic masses of all the atoms in the formula
• b) Multiply the atomic number of the elements by Avogadro’s number
• c) Add the number of protons in each atom
• d) Multiply the total number of molecules by 6.022 × 10²³

32. What is the main characteristic of a chemical reaction?

• a) A change in the physical state of a substance
• b) The creation of new atoms
• c) The formation of new substances with different properties
• d) The separation of a mixture into its components