Question 1

According to the law of conservation of mass, what must be true for any balanced chemical reaction?

Accepted Answer

The total mass of the reactants is equal to the total mass of the products.

Question 2

In the reaction $$4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$$, how many moles of $$Fe_2O_3$$ are produced from 8.0 moles of $$Fe$$?

Accepted Answer

$$4.0$$ moles

Question 3

A student burns $$18.6 g of $$ethane ($$C_2H_6) in $$excess oxygen. Using the equation $$2C_2H_6(g) + 7O_2(g) \rightarrow 4CO_2(g) + 6H_2O(g)$$, how many grams of $$CO_2$$ are produced?

Accepted Answer

$$54.4 g$$

Question 4

Which of the following best describes a limiting reactant in a chemical reaction?

Accepted Answer

It is the reactant that is completely consumed first, thus limiting the amount of product formed.

Question 5

Given the reaction $$C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)$$, how many grams of $$H_2O$$ are produced from $$35.8 g of$$ $$C_3H_8$$?

Accepted Answer

$$58.4 g$$

Question 6

If $$0.400$$ mole of $$Fe_2O_3 is $$produced in the reaction $$4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$$, how many grams of $$O_2$$ are required?

Accepted Answer

$$19.2 g$$

Question 7

A reaction has a theoretical yield of $$88.0 g$$ $$CO_2$$, but only $$72.4 g is $$actually produced. What is the percent yield?

Accepted Answer

$$82.3\%$$

Question 8

Which of the following statements is true for an exothermic reaction?

Accepted Answer

The energy of the products is less than the energy of the reactants, and $$\Delta H is $$negative.

Question 9

In the reaction $$B_2O_3(l) + 3Mg(s) \rightarrow 2B(s) + 3MgO(s)$$, if $$2350 g of$$ $$B_2O_3$$ and $$3580 g of$$ $$Mg$$ are reacted, what is the theoretical yield of $$B$$?

Accepted Answer

$$729 g$$

Question 10

Which of the following is the correct sequence of steps for a mass-to-mass calculation in a chemical reaction?

Accepted Answer

Convert grams of A to moles of A, use the mole-mole factor to find moles of B, then convert moles of B to grams of B.

Question 11

A reaction absorbs heat from the surroundings and has a positive $$\Delta H. $$Which type of reaction is this?

Accepted Answer

Endothermic

Question 12

If $$50.0 g of$$ $$LiOH$$ produces $$72.8 g of$$ $$LiHCO_3 in $$the reaction $$LiOH(s) + CO_2$(g) \rightarrow $$LiHCO_3$$(s)$$, and the theoretical yield is $$142 g$$, what is the percent yield?

Accepted Answer

$$51.3\%$$

Question 13

Which of the following best describes the role of a mole-mole factor in a chemical equation?

Accepted Answer

It is the ratio of the moles of two substances in a balanced chemical equation.

Question 14

A welder uses a torch that burns acetylene ($$C_2H_2) in $$oxygen. If $$26.0 g of$$ $$C_2H_2 is $$burned and the theoretical yield of $$CO_2 is$$ $$88.0 g$$, but only $$72.4 g is $$collected, what is the percent yield?

Accepted Answer

$$82.3\%$$

Question 15

Which of the following is NOT a correct statement about the law of conservation of mass?

Accepted Answer

The total mass of the products is always less than the total mass of the reactants.

Question 16

In a chemical reaction, if the actual yield is less than the theoretical yield, what could be a possible reason?

Accepted Answer

Some product was lost during the process, or the reaction was incomplete.

Question 17

Which of the following reactions is exothermic?

Accepted Answer

$$H_2(g$$) + $$Cl_2(g$$) \rightarrow 2HCl(g) + 185\ kJ$$

Question 18

A student wants to make pancakes using the recipe: 1 cup flour + 2 eggs + 1/2 tsp baking powder = 5 pancakes. If the student has 3 cups of flour, 4 eggs, and 2 tsp baking powder, what is the limiting reactant?

Accepted Answer

Eggs

Question 19

Which of the following best describes the sign of $$\Delta H$$ for an endothermic reaction?

Accepted Answer

Positive

Question 20

In the reaction $$2Ag(s) + S(s) \rightarrow Ag_2S(s)$$, if you start with $$2$$ mol of $$Ag$$ and $$1$$ mol of $$S$$, what is the total mass of the reactants if the molar masses are $$107.9 g/$$mol for $$Ag$$ and $$32.1 g/$$mol for $$S$$?

Accepted Answer

$$247.9 g$$

Chemical Quantities in Reactions: A Study Guide

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