Q: Which of the following is the correct calculation for the enthalpy change ($$\Delta H) of $$the reaction $$\mathrm{C_3H_8} (g) + 5\ \mathrm{O_2$} (g) \rightarrow 3\ \mathrm{CO_2$} (g) + 4\ \mathrm{H_2O} (l)$$ using the provided heats of formation?

$$\Delta H = [3 \times (-393.5) + 4 \times (-285.8)] - [(-104) + 5 \times 0]$$

Question 1

Which of the following best explains why $$\mathrm{CO_2$} is a $$greenhouse gas, but $$\mathrm{N_2$}$$ and $$\mathrm{O_2$}$$ are not?

Accepted Answer

$$\mathrm{CO_2$}$$ absorbs infrared radiation due to symmetry breaking in its vibrational modes, while $$\mathrm{N_2$}$$ and $$\mathrm{O_2$} do $$not have symmetry breaking in their vibrations.

Question 2

A solution is prepared by dissolving $$0.50\ \mathrm{mol} of$$ $$\mathrm{NaCl} in $$enough water to make $$1.0\ \mathrm{L} of $$solution. What is the molarity of the solution?

Accepted Answer

$$0.50\ \mathrm{M}$$

Question 3

Which of the following is the correct balanced equation for the complete combustion of propane, $$\mathrm{C_3H_8}$$?

Accepted Answer

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

Question 4

A student mixes $$50.0\ \mathrm{mL} of$$ $$0.200\ \mathrm{M}$$ $$\mathrm{$$AgNO_3$$}$$ with $$50.0\ \mathrm{mL} of$$ $$0.200\ \mathrm{M}$$ $$\mathrm{NaCl}. $$What is the net ionic equation for the reaction that occurs?

Accepted Answer

$$\mathrm{Ag^+} (aq) + \mathrm{Cl^-} (aq) \rightarrow \mathrm{AgCl} (s)$$

Question 5

Which of the following statements about electrolytes is correct?

Accepted Answer

A strong electrolyte completely dissociates into ions in water, while a weak electrolyte only partially dissociates.

Question 6

Which of the following is the correct expression for Beer's Law, relating absorbance ($$A) to $$concentration ($$c$$)?

Accepted Answer

$$A = \varepsilon b c$$

Question 7

A reaction has a theoretical yield of $$10.0\ \mathrm{g}$$, but only $$7.5\ \mathrm{g} of $$product is recovered. What is the percent yield?

Accepted Answer

$$75\%$$

Question 8

Which of the following is a formation reaction?

Accepted Answer

$$\mathrm{C} (s) + 2\ \mathrm{H_2$} (g) \rightarrow \mathrm{CH_4$} (g)$$

Question 9

Which of the following best describes the sign conventions for $$q$$ and $$w in $$the First Law of Thermodynamics ($$\Delta E = q + w$$)?

Accepted Answer

$$q is $$positive when heat is absorbed by the system; $$w is $$positive when work is done on the system.

Question 10

Which of the following compounds is insoluble in water according to the abbreviated solubility rules?

Accepted Answer

$$\mathrm{$$PbCl_2$$}$$

Question 11

A $$100.0\ \mathrm{g}$$ sample of water is heated from $$25.0^\circ\mathrm{C} to$$ $$75.0^\circ\mathrm{C}. If $$the specific heat of water is $$4.18\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}$$, how much heat is absorbed?

Accepted Answer

$$20,900\ \mathrm{J}$$

Question 12

Which of the following is the correct net ionic equation for the neutralization of $$\mathrm{HCl}$$ with $$\mathrm{NaOH}$$?

Accepted Answer

$$\mathrm{H^+} (aq) + \mathrm{OH^-} (aq) \rightarrow \mathrm{H_2O} (l)$$

Question 13

Which of the following is a state function?

Accepted Answer

Enthalpy ($$\Delta H)$$

Question 14

Which of the following best describes the role of water as a solvent in biological and environmental systems?

Accepted Answer

Water's polarity allows it to dissolve a wide variety of ionic and molecular substances, making it essential for life and environmental processes.

Question 15

Which of the following is the correct calculation for the enthalpy change ($$\Delta H) of $$the reaction $$\mathrm{C_3H_8} (g) + 5\ \mathrm{O_2$} (g) \rightarrow 3\ \mathrm{CO_2$} (g) + 4\ \mathrm{H_2O} (l)$$ using the provided heats of formation?

Accepted Answer

$$\Delta H = [3 	imes (-393.5) + 4 	imes (-285.8)] - [(-104) + 5 	imes 0]$$

Question 16

Which of the following best describes an oxidizing agent in a redox reaction?

Accepted Answer

It is reduced and causes another substance to be oxidized.

Question 17

A $$25.0\ \mathrm{mL}$$ sample of $$0.100\ \mathrm{M}$$ $$\mathrm{H_2SO_4} is $$titrated with $$0.200\ \mathrm{M}$$ $$\mathrm{NaOH}. $$What volume of $$\mathrm{NaOH} is $$required to reach the equivalence point?

Accepted Answer

$$25.0\ \mathrm{mL}$$

Question 18

Which of the following best describes pressure-volume work ($$w = -P\Delta V) in $$the context of an internal combustion engine?

Accepted Answer

The expanding gases do work on the piston, so $$w is $$negative for the system.

Question 19

Which of the following is the correct oxidation number for nitrogen in $$\mathrm{NO_2$}$$?

Accepted Answer

$$+4$$

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