Question 1

Consider the chemical reaction shown in the image: $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}. $$Which of the following statements best explains why the coefficients '2' are used in front of $$\mathrm{O_2$}$$ and $$\mathrm{H_2O} in $$the balanced equation?

Accepted Answer

To ensure that the number of oxygen atoms is the same on both sides of the equation, demonstrating the conservation of mass.

Question 2

In the reaction $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$, how many total molecules of products are formed from one molecule of methane?

Accepted Answer

Three molecules (1 $$\mathrm{CO_2$}$$ and 2 $$\mathrm{H_2O})$$

Question 3

Which observation would best indicate that the reaction $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$ has occurred?

Accepted Answer

Formation of water vapor and release of heat.

Question 4

If you start with 2 moles of methane ($$\mathrm{CH_4$}) $$and excess oxygen, how many moles of water ($$\mathrm{H_2O}) $$will be produced according to the balanced equation $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$?

Accepted Answer

4 moles

Question 5

Why is it incorrect to write the equation for methane combustion as $$\mathrm{CH_4$ + O_2$ \rightarrow CO_2$ + H_2O}$$ without coefficients?

Accepted Answer

Because the number of oxygen atoms is not balanced on both sides of the equation.

Question 6

Which of the following best describes the role of coefficients in a balanced chemical equation?

Accepted Answer

They indicate the relative number of molecules or moles of each substance involved in the reaction.

Question 7

In the balanced equation $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$, what is the total number of oxygen atoms on the reactant side?

Accepted Answer

4

Question 8

Which of the following is a correct interpretation of the arrow ($$\rightarrow) in $$the chemical equation $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$?

Accepted Answer

It means 'yields' or 'produces', indicating the direction of the reaction from reactants to products.

Question 9

If the physical states are included, which is the correct way to write the balanced equation for the combustion of methane?

Accepted Answer

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

Question 10

Which of the following best explains why the subscripts in chemical formulas (e.g., the '2' in $$\mathrm{H_2O}) $$must not be changed when balancing equations?

Accepted Answer

Changing subscripts would alter the chemical identity of the substance.

Chemical Reactions and Balancing Chemical Equations

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