Question 1

Which of the following best describes a chemical reaction?

Accepted Answer

A process in which one or more substances are converted into different substances, involving chemical changes in matter.

Question 2

What is the correct balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4(g) + 2O_2(g$$) \rightarrow $$CO_2(g) + 2H_2O(g$$)$$

Question 3

In a balanced chemical equation, why is it incorrect to change the subscripts in chemical formulas to balance the equation?

Accepted Answer

Changing subscripts alters the identity of the substance, creating a different compound.

Question 4

Which of the following is the correct balanced equation for the reaction of solid silicon dioxide ($$SiO_2) $$with solid carbon ($$C) to $$produce solid silicon carbide ($$SiC) $$and carbon monoxide gas ($$CO$$)?

Accepted Answer

$$SiO_2(s) + 3C(s$$) \rightarrow SiC(s) + 2CO(g)$$

Question 5

When balancing the combustion of ethane ($$C_2H_6$$), which of the following is the correct set of coefficients for the equation: $$C_2H_6(g) + O_2$(g) \rightarrow CO_2$(g) + H_2O(g)$$?

Accepted Answer

$$2C_2H_6(g) + 7O_2(g) \rightarrow 4CO_2(g) + 6H_2O(g)$$

Question 6

A student is balancing the following equation: $$Fe_2O_3(s) + CO(g) \rightarrow Fe(s) + CO_2$(g). $$What is the correct balanced equation?

Accepted Answer

$$Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)$$

Question 7

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

The number of atoms of each element must be the same on both sides of the equation.

Question 8

In the reaction $$SrCl_2(aq) + Li_3PO_4(aq$$) \rightarrow $$Sr_3$$($$PO_4)_2(s) + $$LiCl(aq)$$, what is the correct set of coefficients to balance the equation?

Accepted Answer

$$3SrCl_2(aq) + 2Li_3PO_4(aq) \rightarrow Sr_3$(PO_4$)_2(s) + 6LiCl(aq)$$

Question 9

A propane grill uses the combustion of propane ($$C_3H_8) $$for cooking. What is the balanced equation for the complete combustion of propane in oxygen?

Accepted Answer

$$C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)$$

Question 10

Which of the following best explains why coefficients are used when balancing chemical equations?

Accepted Answer

Coefficients adjust the number of molecules or formula units to ensure the law of conservation of mass is obeyed.

Question 11

A student writes the following unbalanced equation for the combustion of butane ($$C_4H_{10}$$): $$C_4H_{10}(g) + O_2$(g) \rightarrow CO_2$(g) + H_2O(g). $$What is the correct balanced equation?

Accepted Answer

$$2C_4H_{10}(g) + 13O_2(g) \rightarrow 8CO_2(g) + 10H_2O(g)$$

Question 12

Which of the following is a correct statement about the use of polyatomic ions when balancing chemical equations?

Accepted Answer

If a polyatomic ion appears unchanged on both sides of the equation, it can be balanced as a unit.

Question 13

A real-world application: In the steel industry, iron(III) oxide reacts with carbon monoxide to produce iron and carbon dioxide. What is the balanced equation for this reaction?

Accepted Answer

$$Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)$$

Question 14

Which of the following is the correct balanced equation for the reaction of solid calcium with water to produce calcium hydroxide and hydrogen gas?

Accepted Answer

$$Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2$(g)$$

Question 15

A hospital uses hydrogen peroxide ($$H_2O_2) as a $$disinfectant. When it decomposes, it forms water and oxygen gas. What is the balanced equation for this decomposition?

Accepted Answer

$$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2$(g)$$

Question 16

Which of the following is the correct balanced equation for the reaction of aluminum with oxygen to form aluminum oxide?

Accepted Answer

$$4Al(s) + 3O_2(g) \rightarrow 2Al_2O_3(s)$$

Question 17

A student is asked to balance the following equation: $$KClO_3(s$$) \rightarrow KCl(s) + $$O_2(g$$)$$. What is the correct balanced equation?

Accepted Answer

$$2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$$

Writing and Balancing Chemical Equations

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