Chemical Reactions

​ (a)   C₂H₆ + ​ (b)   O₂ --> ​ (c)   H₂O + ​ (d)   CO₂

• 7

• 6

• 2

• 4

Answer explanation

To balance the combustion of ethane (C2H6), we need 7 O2 to produce 6 H2O and 4 CO2. The balanced equation is: 2 C2H6 + 7 O2 -> 6 H2O + 4 CO2, confirming the correct coefficients are 7, 6, 2, and 4.

​ (a)   HClO₄ + P₄O₁₀ --> ​ (b)   H₃PO₄ + ​ (c)   Cl₂O₇

• 12

• 4

• 6

Answer explanation

In the reaction, 12 HClO4 reacts with 4 P4O10 to produce 6 H3PO4 and 12 Cl2O7. The coefficients balance the equation, confirming that the correct choices are 12, 4, and 6.

​ (a)   N₂ + ​ (b)   O₂ + 2H₂O --> ​ (c)   HNO₃

• 2

• 5

• 4

• 3

• 6

Answer explanation

In the balanced equation, 2 moles of N2 react with 5 moles of O2 and 2 moles of H2O to produce 4 moles of HNO3. Therefore, the correct answer for the blank before HNO3 is 4.

​ (a)   CaCl₂ + ​ (b)   Na₃PO₄ --> Ca₃(PO₄)₂ + ​ (c)   NaCl

• 3

• 2

• 6

• 4

Answer explanation

In the reaction, 3 moles of CaCl2 react with 2 moles of Na3PO4 to produce 1 mole of Ca3(PO4)2 and 6 moles of NaCl. The coefficients balance the equation, confirming the correct choices are 3, 2, and 6.

​ (a)   FeS + ​ (b)   O₂ --> ​ (c)   Fe₂O₃ + 4SO₂

• 4

• 7

• 2

• 3

Answer explanation

In the reaction, 4 moles of FeS react with 7 moles of O2 to produce 2 moles of Fe2O3 and 4 moles of SO2. The coefficients balance the equation, confirming that the correct answer is 4 for FeS.

​ (a)   C₃H₈ + ​ (b)   O₂ --> ​ ​ (c)   CO₂ + ​ (d)   H₂O

• 1

• 5

• 4

• 3

• 2

Answer explanation

The balanced equation for the combustion of propane (C3H8) requires 5 O2 molecules to produce 3 CO2 and 4 H2O. Thus, the correct coefficients are 1 for C3H8, 5 for O2, 3 for CO2, and 4 for H2O.

What is the missing coefficient?
__SeCl + 2O₂ --> 2SeO₂ + Cl₂

• 1

• 2

• 3

• 4

Answer explanation

To balance the equation, we need 2 SeCl to produce 2 SeO2 and 1 Cl2. Thus, the missing coefficient for SeCl is 2, ensuring the number of each atom is equal on both sides of the reaction.

15.6 grams of lead(II) nitrate is in a test tube. A 4.8-g sample of potassium iodide is an Erlenmeyer flask. The substance in the test tube is poured into the Erlenmeyer flask so that the two substances react. What is the mass of the combined products?

• 20.4 g

• 10.8 g

• 4.8 g

• 136 g

Answer explanation

The total mass of the reactants is 15.6 g (lead(II) nitrate) + 4.8 g (potassium iodide) = 20.4 g. According to the law of conservation of mass, the mass of the products equals the mass of the reactants, so the correct answer is 20.4 g.

Pb(NO₃)₂ + 2KI --> PbI₂ + __KNO₃

• 1

• 2

• 3

• 4

Answer explanation

In the reaction, 1 mole of Pb(NO3)2 reacts with 2 moles of KI to produce 1 mole of PbI2 and 2 moles of KNO3. Therefore, the correct answer is 2, indicating 2 moles of KNO3 are produced.

HCl + NaOH --> NaCl + H₂O

Groups:

(a) Products

,

(b) Reactants

• H₂O

• HCl

• NaCl

• NaOH