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

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

Q: A student mixes 28.5 g KCl with 25.7 g Pb$$^{2+}$$ and obtains 29.4 g PbCl$$_2 as a $$precipitate. What is the percent yield if the theoretical yield is 34.5 g?

$$\displaystyle \frac{29.4}{34.5} \times 100\% = 85.2\%$$

Question 1

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

Accepted Answer

The reactant that is completely consumed and determines the maximum amount of product formed.

Question 2

Given the unbalanced equation: $$\mathrm{C_3H_8(g) + O_2$(g) \rightarrow CO_2$(g) + H_2O(g)}$$, what is the correct balanced equation?

Accepted Answer

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

Question 3

Which of the following is the correct sequence for a mass-to-mass stoichiometry calculation?

Accepted Answer

Mass A $$\rightarrow$$ Amount A (in moles) $$\rightarrow$$ Amount B (in moles) $$\rightarrow$$ Mass B

Question 4

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

Accepted Answer

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

Question 5

Which of the following best describes the physical state notation (aq) in a chemical equation?

Accepted Answer

Aqueous (dissolved in water)

Question 6

In the reaction $$2 \mathrm{Na(s)} + \mathrm{Br_2$(g)} \rightarrow 2 \mathrm{NaBr(s)}$$, if you start with 3.0 mol Na and 1.0 mol Br$$_2$$, which is the limiting reactant?

Accepted Answer

Br$$_2$$

Question 7

Which of the following is true about balancing chemical equations?

Accepted Answer

You should balance atoms in complex substances before pure elements.

Question 8

What is the product of the combustion of methane ($$\mathrm{CH_4$}) in $$oxygen?

Accepted Answer

$$\mathrm{CO_2$}$$ and $$\mathrm{H_2O}$$

Question 9

If 4.2 mol ZnS and 6.8 mol O$$_2$$ react according to $$2 \mathrm{ZnS(s)} + 3 \mathrm{O_2$(g)} \rightarrow 2 \mathrm{ZnO(s)} + 2 \mathrm{SO_2$(g)}$$, how many moles of O$$_2$$ remain after the reaction is complete?

Accepted Answer

0.5 mol

Question 10

Which of the following reactions is an example of a combustion reaction?

Accepted Answer

$$\mathrm{2 H_2$(g) + O_2$(g) \rightarrow 2 H_2O(g)}$$

Question 11

Which of the following statements about alkali metals reacting with water is correct?

Accepted Answer

The reaction produces a metal hydroxide and hydrogen gas.

Question 12

What is the balanced equation for the reaction of solid lithium with liquid water?

Accepted Answer

$$\mathrm{2 Li(s) + 2 H_2O(l) \rightarrow 2 LiOH(aq) + H_2$(g)}$$

Question 13

A student mixes 28.5 g KCl with 25.7 g Pb$$^{2+}$$ and obtains 29.4 g PbCl$$_2 as a $$precipitate. What is the percent yield if the theoretical yield is 34.5 g?

Accepted Answer

$$\displaystyle \frac{29.4}{34.5} 	imes 100\% = 85.2\%$$

Question 14

Which of the following is NOT a correct guideline for balancing chemical equations?

Accepted Answer

Change the subscripts in chemical formulas to balance the equation.

Question 15

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

Accepted Answer

They specify the relative amounts in moles of each substance in the reaction.

Question 16

Which of the following is the correct balanced equation for the reaction of solid strontium with iodine gas?

Accepted Answer

$$\mathrm{Sr(s) + I_2$(g) \rightarrow $$SrI_2$$(s)}$$

Question 17

Which of the following is a correct statement about combustion reactions involving hydrocarbons?

Accepted Answer

They always produce carbon dioxide and water.

Question 18

In a chemical equation, what does the arrow ($$\rightarrow) $$represent?

Accepted Answer

The direction of the chemical reaction, from reactants to products.

Question 19

If you have 10.0 g of A and 20.0 g of B, and the balanced equation is $$A + 2B \rightarrow C$$, which reactant is limiting if the molar masses are $$M_A = 5.0 g/$$mol and $$M_B = 10.0 g/$$mol?

Accepted Answer

B

Chemical Reactions and Chemical Quantities: Structured Study Notes

Guida di studio - Domande di pratica

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