Q: Given the reaction: $$2 \text{H}_2 + \text{O}_2 \rightarrow 2 \text{H}_2\text{O}$$, how many grams of water can be produced from 5.0 g of $$\text{H}_2$$ and excess $$\text{O}_2$$? (Molar mass of $$\text{H}_2 = 2.02 g/$$mol, $$\text{H}_2\text{O} = 18.02 g/$$mol)

5.0 \text{ g } \times \frac{1 \text{ mol } \text{H}_2}{2.02 \text{ g } \text{H}_2} \times \frac{2 \text{ mol } \text{H}_2\text{O}}{2 \text{ mol } \text{H}_2} \times \frac{18.02 \text{ g } \text{H}_2\text{O}}{1 \text{ mol } \text{H}_2\text{O}} = 44.55 \text{ g } \text{H}_2\text{O}

Question 1

Which of the following best describes Avogadro's number?

Accepted Answer

The number of units (atoms, molecules, ions) in 1 mole of a substance, $$6.022 	imes 10$$^{23}$$

Question 2

A sample contains 63.55 g of copper (Cu). How many moles of copper are present? (Atomic mass of Cu = 63.55 g/mol)

Accepted Answer

$$\frac{63.55}{63.55}$$ moles = 1 mole

Question 3

Which statement about the Law of Conservation of Mass is correct?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction

Question 4

Given the reaction: $$2 	ext{H}_2 + 	ext{O}_2 ightarrow 2 	ext{H}_2	ext{O}$$, how many grams of water can be produced from 5.0 g of $$	ext{H}_2$$ and excess $$	ext{O}_2$$? (Molar mass of $$	ext{H}_2 = 2.02 g/$$mol, $$	ext{H}_2	ext{O} = 18.02 g/$$mol)

Accepted Answer

5.0 	ext{ g } 	imes \frac{1 	ext{ mol } 	ext{H}_2}{2.02 	ext{ g } 	ext{H}_2} 	imes \frac{2 	ext{ mol } 	ext{H}_2	ext{O}}{2 	ext{ mol } 	ext{H}_2} 	imes \frac{18.02 	ext{ g } 	ext{H}_2	ext{O}}{1 	ext{ mol } 	ext{H}_2	ext{O}} = 44.55 	ext{ g } 	ext{H}_2	ext{O}

Question 5

Which of the following is true for an exothermic reaction?

Accepted Answer

$$q \u003c 0$$, $$\Delta H \u003c 0$$, heat is released

Question 6

A reaction has $$\Delta H = +100 kJ $$and $$\Delta S = +200 J/K. At $$what temperature will the reaction become spontaneous? (Use $$\Delta G = \Delta H - T\Delta S)$$

Accepted Answer

At high temperatures, when $$T \u003e \frac{\Delta H}{\Delta S}$$

Question 7

Which of the following best describes entropy ($$S$$)?

Accepted Answer

The measure of disorder or randomness in a system

Question 8

If the equilibrium constant $$K_{eq}$$ for a reaction is much greater than 1, what does this indicate?

Accepted Answer

The reaction favors products

Question 9

Which of the following will increase the rate of a chemical reaction?

Accepted Answer

Adding a catalyst

Question 10

What is the empirical formula for a compound containing 43.64% phosphorus and 56.36% oxygen? (Atomic masses: P = 30.97 g/mol, O = 16.00 g/mol)

Accepted Answer

$$	ext{P}_2	ext{O}_5$$

Question 11

Which of the following is NOT a correct step in calculating the empirical formula from percent composition?

Accepted Answer

Multiply all mole values by Avogadro's number

Question 12

Which statement about activation energy ($$E_a) is $$correct?

Accepted Answer

It is the energy required to initiate a chemical reaction

Question 13

For the reaction $$aA + bB \rightleftharpoons cC + dD$$, the equilibrium constant expression is:

Accepted Answer

$$K_{eq} = \frac{[C]^c [D]^d}{[A]^a [B]^b}$$

Question 14

Which of the following changes will shift the equilibrium of an exothermic reaction to the left?

Accepted Answer

Increasing the temperature

Question 15

If a reaction is spontaneous, which of the following must be true?

Accepted Answer

$$\Delta G \u003c 0$$

Question 16

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$$\% = \frac{	ext{actual}}{	ext{theoretical}} 	imes 100$$

Question 17

Which of the following statements about catalysts is correct?

Accepted Answer

Catalysts lower the activation energy but do not change the equilibrium composition

Question 18

Which of the following is true about dynamic equilibrium?

Accepted Answer

The rates of the forward and reverse reactions are equal

Question 19

Which of the following is a correct statement about the relationship between thermodynamics and kinetics?

Accepted Answer

Thermodynamics determines if a reaction can occur, kinetics determines how fast it occurs

GOB Chemistry: Mole, Mass Relationships, Thermodynamics, and Chemical Equilibrium

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