Q: Which of the following is the correct relationship for the enthalpy change ($$\Delta H) of a $$reaction?

$$\Delta H = \text{products} - \text{reactants}$$

Question 1

Which of the following best describes a chemical change?

Accepted Answer

Iron rusting when exposed to air

Question 2

A sample of gas occupies $$2.50\ \mathrm{L} at$$ $$1.00\ \mathrm{atm}$$ and $$300\ \mathrm{K}. $$What will be its volume at $$2.00\ \mathrm{atm}$$ and $$400\ \mathrm{K}$$? (Assume ideal gas behavior.)

Accepted Answer

$$1.67\ \mathrm{L}$$

Question 3

Which of the following statements about Avogadro's number is correct?

Accepted Answer

It is the number of molecules in $$1\ \mathrm{mol} of $$any substance.

Question 4

Which of the following compounds contains both ionic and covalent bonds?

Accepted Answer

$$\mathrm{$$NaNO_3$$}$$

Question 5

A $$5.00\ \mathrm{g}$$ sample of magnesium reacts with excess oxygen to form magnesium oxide. What is the theoretical yield of $$\mathrm{MgO}$$? (Molar mass: $$\mathrm{Mg} = 24.3\ \mathrm{g/mol}$$, $$\mathrm{O} = 16.0\ \mathrm{g/mol})$$

Accepted Answer

$$6.67\ \mathrm{g}$$

Question 6

Which of the following best explains why water has a higher boiling point than methane ($$\mathrm{CH_4$}$$)?

Accepted Answer

Water forms hydrogen bonds, while methane does not.

Question 7

Which of the following electron configurations represents a noble gas?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$

Question 8

A balloon filled with $$2.00\ \mathrm{mol} of $$helium at $$300\ \mathrm{K}$$ and $$1.00\ \mathrm{atm} is $$released and rises to a region where the pressure is $$0.500\ \mathrm{atm}$$ and the temperature is $$250\ \mathrm{K}. $$What is the new volume if the initial volume was $$49.2\ \mathrm{L}$$?

Accepted Answer

$$82.0\ \mathrm{L}$$

Question 9

Which of the following best describes the quantum mechanical model of the atom?

Accepted Answer

Electrons are found in specific energy levels but not in defined orbits.

Question 10

Which of the following molecules has a trigonal planar geometry?

Accepted Answer

$$\mathrm{BF_3$}$$

Question 11

Which of the following is the correct Lewis structure for $$\mathrm{CO_2$}$$?

Accepted Answer

O=C=O, with each O atom having two lone pairs

Question 12

Which of the following best explains why sodium chloride ($$\mathrm{NaCl}) $$conducts electricity when dissolved in water but not as a solid?

Accepted Answer

The ions are free to move in solution but fixed in the solid.

Question 13

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have the same number of valence electrons.

Question 14

A $$50.0\ \mathrm{g}$$ sample of water at $$25.0\ ^\circ\mathrm{C}$$ absorbs $$4180\ \mathrm{J} of $$heat. What is the final temperature? (Specific heat of water $$= 4.18\ \mathrm{J/g\cdot ^\circ C})$$

Accepted Answer

$$35.0\ ^\circ\mathrm{C}$$

Question 15

Which of the following best describes the concept of resonance in Lewis structures?

Accepted Answer

A molecule has a single structure with delocalized electrons.

Question 16

Which of the following gases will diffuse the fastest at room temperature?

Accepted Answer

$$\mathrm{H_2$}$$

Question 17

Which of the following best explains why ice floats on liquid water?

Accepted Answer

Hydrogen bonding causes ice to have an open, hexagonal structure.

Question 18

Which of the following is the correct relationship for the enthalpy change ($$\Delta H) of a $$reaction?

Accepted Answer

$$\Delta H = 	ext{products} - 	ext{reactants}$$

Question 19

Which of the following best describes the effect of increasing temperature on the rate of a chemical reaction?

Accepted Answer

It increases the frequency and energy of molecular collisions.

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