Q: Which of the following is the correct formula for calculating the energy change for a reaction using bond energies?

$$\Delta H = \sum \text{bond energies of reactants} - \sum \text{bond energies of products}$$

Question 1

Which of the following best explains why sodium (Na) and potassium (K) have similar chemical properties?

Accepted Answer

They have the same number of valence electrons.

Question 2

Given the formula $$\mathrm{$$CaCl_2$$}$$, what is the correct name for this compound?

Accepted Answer

Calcium chloride

Question 3

Which of the following statements about ionization energy is correct?

Accepted Answer

Ionization energy increases across a period from left to right.

Question 4

A sample contains $$2.50$$ moles of $$\mathrm{NaCl}. $$What is the mass of the sample? ($$\mathrm{Na} = 23.0\ \mathrm{g/mol}$$, $$\mathrm{Cl} = 35.5\ \mathrm{g/mol})$$

Accepted Answer

$$146.25\ \mathrm{g}$$

Question 5

Which of the following is an example of an endothermic process?

Accepted Answer

Evaporation of alcohol

Question 6

What is the empirical formula for a compound containing $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 7

Which of the following best describes the difference between ionic and covalent bonds?

Accepted Answer

Ionic bonds involve the transfer of electrons, while covalent bonds involve the sharing of electrons.

Question 8

Calculate the enthalpy change for the reaction: $$\mathrm{2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)}$$, given $$\Delta H_f^\circ$$ for $$\mathrm{H_2O(l)} is$$ $$-285.8\ \mathrm{kJ/mol}.$$

Accepted Answer

$$-571.6\ \mathrm{kJ}$$

Question 9

Which of the following compounds is polar?

Accepted Answer

$$\mathrm{NH_3$}$$

Question 10

A student mixes $$50.0\ \mathrm{mL} of$$ $$1.0\ \mathrm{M}$$ $$\mathrm{HCl}$$ with $$50.0\ \mathrm{mL} of$$ $$1.0\ \mathrm{M}$$ $$\mathrm{NaOH}. $$What is the final concentration of $$\mathrm{NaCl} in $$the solution?

Accepted Answer

$$0.5\ \mathrm{M}$$

Question 11

Which of the following best explains why water has a higher boiling point than methane?

Accepted Answer

Water forms hydrogen bonds, which are stronger than the forces in methane.

Question 12

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

Accepted Answer

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

Question 13

Which of the following statements about semiconductors is correct?

Accepted Answer

Semiconductors have a small band gap between the valence and conduction bands.

Question 14

Which of the following best describes the difference between a saturated and unsaturated solution?

Accepted Answer

A saturated solution contains more solute than an unsaturated solution.

Question 15

Which of the following is the correct formula for calculating the energy change for a reaction using bond energies?

Accepted Answer

$$\Delta H = \sum 	ext{bond energies of reactants} - \sum 	ext{bond energies of products}$$

Question 16

Which of the following is NOT a type of intermolecular force?

Accepted Answer

Ionic bonding

Question 17

Which of the following best explains why ionic compounds tend to have high melting points?

Accepted Answer

Ionic compounds have strong electrostatic attractions between ions.

Question 18

Which of the following is the correct electron configuration for $$\mathrm{O} ($$oxygen, atomic number 8)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^4$$

Question 19

Which of the following statements about band gaps in solids is correct?

Accepted Answer

Semiconductors have a moderate band gap.

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