Q: A reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is obtained. What is the percent yield?

$$ \frac{7.5}{10.0} \times 100\% = 75\% $$

Question 1

Which of the following best describes a balanced chemical equation?

Accepted Answer

An equation in which the total number of each type of atom on the reactant side equals the total number on the product side.

Question 2

In the chemical equation $$ \mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)} $$, what is the role of $$ \mathrm{O_2$} $$?

Accepted Answer

It is a reactant that combines with methane in a combustion reaction.

Question 3

Which symbol in a chemical equation indicates that a substance is dissolved in water?

Accepted Answer

$$ (aq) $$

Question 4

A student is balancing the equation $$ \mathrm{C_2H_6 + O_2$ \rightarrow CO_2$ + H_2O} . $$What is the correct first step according to the balancing strategy?

Accepted Answer

Balance the carbon atoms first.

Question 5

Which of the following is a correct statement about limiting reactants?

Accepted Answer

The limiting reactant is the one that is entirely consumed when the reaction goes to completion.

Question 6

In a combustion reaction involving a hydrocarbon, what are the typical products?

Accepted Answer

Carbon dioxide and water

Question 7

Which of the following best explains why actual yield is often less than theoretical yield?

Accepted Answer

Side reactions and incomplete reactions can reduce the amount of product formed.

Question 8

Given the reaction $$ \mathrm{2H_2(g) + O_2$(g) \rightarrow 2H_2O(g)} $$, how many moles of $$ \mathrm{H_2O} $$ are produced from 4 moles of $$ \mathrm{H_2$} $$ and excess $$ \mathrm{O_2$} $$?

Accepted Answer

4 moles

Question 9

Which of the following is NOT a valid strategy for balancing chemical equations?

Accepted Answer

Change the chemical formula of a reactant to achieve balance.

Question 10

A reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is obtained. What is the percent yield?

Accepted Answer

$$ \frac{7.5}{10.0} 	imes 100\% = 75\% $$

Question 11

Which of the following best describes a hydrocarbon?

Accepted Answer

A compound composed only of hydrogen and carbon.

Question 12

What is the mole-to-mole ratio of $$ \mathrm{O_2$}  to$$ $$ \mathrm{CO_2$}  in $$the reaction $$ \mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O} $$?

Accepted Answer

$$ 2:1 $$

Question 13

Which of the following is the correct sequence for stoichiometric calculations?

Accepted Answer

Convert mass to moles, use the balanced equation, convert moles to mass.

Question 14

If 3.0 moles of $$ \mathrm{C_2H_6} $$ react with 10.0 moles of $$ \mathrm{O_2$} $$ according to $$ \mathrm{2C_2H_6 + 7O_2 \rightarrow 4CO_2 + 6H_2O} $$, what is the limiting reactant?

Accepted Answer

$$ \mathrm{O_2$} $$

Question 15

Which of the following is a correct statement about excess reactant?

Accepted Answer

It is the reactant that remains after the reaction is complete.

Question 16

In the reaction $$ \mathrm{2H_2 + O_2$ \rightarrow 2H_2O} $$, what is the mole-to-mole ratio of $$ \mathrm{H_2$}  to$$ $$ \mathrm{O_2$} $$?

Accepted Answer

$$ 2:1 $$

Question 17

Which of the following is NOT a reason why actual yield may differ from theoretical yield?

Accepted Answer

All reactants are always converted to products.

Question 18

What does the symbol $$ \Delta $$ above the arrow in a chemical equation indicate?

Accepted Answer

The reaction occurs at high temperature.

Question 19

Which of the following is the general chemical formula for a hydrocarbon?

Accepted Answer

$$ \mathrm{C_xH_y} $$

Question 20

A student needs to balance the equation $$ \mathrm{Fe + O_2$ \rightarrow Fe_2O_3} . $$What is the correct set of coefficients?

Accepted Answer

$$ 4, 3, 2 $$

Chemical Reactions and Chemical Quantities: Study Notes

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