Question 1

Which of the following is the correct first step when balancing a chemical equation according to the guidelines provided?

Accepted Answer

Balance free elements last.

Question 2

Given the unbalanced equation: $$\mathrm{C_2H_4 (g) + O_2$ (g) \rightarrow CO_2$ (g) + H_2O (g)}$$, what is the correct coefficient for $$\mathrm{O_2$}$$ when the equation is balanced?

Accepted Answer

3

Question 3

Why is it recommended to balance molecules where atoms exist in only one place on either side of the arrow before balancing free elements?

Accepted Answer

Because these atoms are easier to track and do not affect other compounds.

Question 4

Balance the following equation: $$\mathrm{NH_3$ (g) + O_2$ (g) \rightarrow N_2$ (g) + H_2O (g)}. $$What is the coefficient for $$\mathrm{NH_3$} in $$the balanced equation?

Accepted Answer

4

Question 5

In the reaction $$\mathrm{Cr (s) + Fe(NO_3$)_2 (aq) \rightarrow Fe(s) + Cr(NO_3$)_3(aq)}$$, which element should be balanced last according to the guidelines?

Accepted Answer

Cr

Question 6

A student balances the equation $$\mathrm{C_2H_4 + O_2$ \rightarrow CO_2$ + H_2O} as$$ $$\mathrm{C_2H_4 + 2O_2 \rightarrow 2CO_2 + 2H_2O}. $$What is the error in this balancing?

Accepted Answer

The number of oxygen atoms is not balanced.

Question 7

Which of the following best describes a 'free element' in the context of balancing equations?

Accepted Answer

An element that appears alone, not bonded to other elements, on one side of the equation.

Question 8

Balance the equation: $$\mathrm{Cr (s) + Fe(NO_3$)_2 (aq) \rightarrow Fe(s) + Cr(NO_3$)_3(aq)}. $$What is the coefficient for $$\mathrm{Fe(NO_3$)_2}$$?

Accepted Answer

2

Question 9

Which of the following is a correct strategy for balancing chemical equations involving polyatomic ions?

Accepted Answer

Treat polyatomic ions as a single unit if they appear unchanged on both sides.

Question 10

A real-world application: The combustion of ethylene ($$\mathrm{C_2H_4}) is $$used in welding torches. What is the balanced equation for the complete combustion of ethylene?

Accepted Answer

$$\mathrm{C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O}$$

Question 11

Which of the following best explains why balancing chemical equations is necessary in real-world chemical manufacturing?

Accepted Answer

To ensure the law of conservation of mass is obeyed and reactants are used efficiently.

Question 12

Balance the equation: $$\mathrm{NH_3$ (g) + O_2$ (g) \rightarrow N_2$ (g) + H_2O (g)}. $$What is the sum of all coefficients in the balanced equation?

Accepted Answer

10

Question 13

If a chemical equation is not balanced, which of the following laws is being violated?

Accepted Answer

Law of Conservation of Mass

Question 14

In the reaction $$\mathrm{NH_3$ + O_2$ \rightarrow N_2$ + H_2O}$$, what is the minimum number of $$\mathrm{O_2$}$$ molecules required to completely react with 4 molecules of $$\mathrm{NH_3$}$$?

Accepted Answer

5

Balancing Chemical Equations: Self Study Assignment

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