Question 1

Which of the following is NOT a sign that a chemical reaction has occurred?

Accepted Answer

The temperature of the mixture remains constant

Question 2

Which observation best indicates that a chemical reaction has taken place when hydrochloric acid is added to zinc metal?

Accepted Answer

Bubbles of gas are produced

Question 3

Balance the following chemical equation: $$ \mathrm{C_2H_6} + \mathrm{O_2$} \rightarrow \mathrm{CO_2$} + \mathrm{H_2O} $$

Accepted Answer

$$ 2\ \mathrm{C_2H_6} + 7\ \mathrm{O_2$} \rightarrow 4\ \mathrm{CO_2$} + 6\ \mathrm{H_2O} $$

Question 4

Balance the following equation: $$ \mathrm{Al} + \mathrm{O_2$} \rightarrow \mathrm{Al_2O_3} $$

Accepted Answer

$$ 4\ \mathrm{Al} + 3\ \mathrm{O_2$} \rightarrow 2\ \mathrm{Al_2O_3} $$

Question 5

Balance the following equation using the 'special method' of fractions: $$ \mathrm{C_3H_8} + \mathrm{O_2$} \rightarrow \mathrm{CO_2$} + \mathrm{H_2O} $$

Accepted Answer

$$ \mathrm{C_3H_8} + 5\ \mathrm{O_2$} \rightarrow 3\ \mathrm{CO_2$} + 4\ \mathrm{H_2O} $$

Question 6

What type of reaction is represented by the following equation? $$ 2\ \mathrm{$$KClO_3$$} \rightarrow 2\ \mathrm{KCl} + 3\ \mathrm{O_2$} $$

Accepted Answer

Decomposition

Question 7

Identify the type of reaction: $$ \mathrm{Zn} + \mathrm{$$CuSO_4$$} \rightarrow \mathrm{$$ZnSO_4$$} + \mathrm{Cu} $$

Accepted Answer

Single displacement

Question 8

Which of the following best defines stoichiometry?

Accepted Answer

The calculation of the quantities of reactants and products in chemical reactions

Question 9

Given the balanced equation $$ 2\ \mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\ \mathrm{H_2O} $$, what is the molar ratio of $$ \mathrm{H_2$}  to$$ $$ \mathrm{O_2$} $$?

Accepted Answer

$$ 2:1 $$

Question 10

How many moles of $$ \mathrm{CO_2$} $$ are produced when 4 moles of $$ \mathrm{C_2H_6} $$ react completely according to the equation $$ 2\ \mathrm{C_2H_6} + 7\ \mathrm{O_2$} \rightarrow 4\ \mathrm{CO_2$} + 6\ \mathrm{H_2O} $$?

Accepted Answer

8 moles

Question 11

If 10.0 g of $$ \mathrm{H_2O} $$ are produced, how many grams of $$ \mathrm{O_2$} $$ were consumed? (Use the balanced equation: $$ 2\ \mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\ \mathrm{H_2O} $$; molar mass $$ \mathrm{H_2O} = 18.0\ \mathrm{g/mol} $$, $$ \mathrm{O_2$} = 32.0\ \mathrm{g/mol} )$$

Accepted Answer

8.89 g

Question 12

Given the reaction $$ \mathrm{N_2$} + 3\ \mathrm{H_2$} \rightarrow 2\ \mathrm{NH_3$} $$, if you have 5.0 mol $$ \mathrm{N_2$} $$ and 12.0 mol $$ \mathrm{H_2$} $$, what is the limiting reagent?

Accepted Answer

$$ \mathrm{H_2$} $$

Question 13

For the reaction $$ 2\ \mathrm{Al} + 3\ \mathrm{Cl_2$} \rightarrow 2\ \mathrm{$$AlCl_3$$} $$, if you start with 4.0 mol $$ \mathrm{Al} $$ and 5.0 mol $$ \mathrm{Cl_2$} $$, what is the limiting reagent?

Accepted Answer

$$ \mathrm{Cl_2$} $$

Question 14

A student performs a reaction and obtains 7.5 g of product. The theoretical yield is 10.0 g. What is the percent yield?

Accepted Answer

$$ 75\% $$

Question 15

In a reaction, 12.0 g of $$ \mathrm{NaCl} $$ are produced, but the theoretical yield is 15.0 g. What is the percent yield?

Accepted Answer

$$ 80\% $$

Question 16

Which statement about enthalpy ($$ \Delta H ) is $$correct?

Accepted Answer

A negative $$ \Delta H $$ indicates an exothermic reaction

Question 17

Which of the following reactions is endothermic?

Accepted Answer

A reaction with $$ \Delta H = +150\ \mathrm{kJ} $$

Question 18

Given the reaction $$ \mathrm{N_2$} + 3\ \mathrm{H_2$} \rightarrow 2\ \mathrm{NH_3$} $$, $$ \Delta H = -92\ \mathrm{kJ} . $$How much heat is released when 6.0 mol $$ \mathrm{NH_3$} $$ are formed?

Accepted Answer

$$ -276\ \mathrm{kJ} $$

Question 19

A reaction has the following balanced equation: $$ 2\ \mathrm{SO_2$} + \mathrm{O_2$} \rightarrow 2\ \mathrm{SO_3$} $$, $$ \Delta H = -198\ \mathrm{kJ} . If 4.0 $$mol $$ \mathrm{SO_2$} $$ react, what is the enthalpy change?

Accepted Answer

$$ -396\ \mathrm{kJ} $$

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