Q: A photon has a wavelength of $500\ \mathrm{nm}$. What is its energy in joules? $(h = 6.626 \times 10^{-34}\ \mathrm{J\cdot s},\ c = 3.00 \times 10^8\ \mathrm{m/s})$

$3.98 \times 10^{-19}\ \mathrm{J}$

Question 1

Which of the following statements best describes the difference between an extensive and an intensive property? Choose the correct example for each.

Accepted Answer

Extensive properties depend on the amount of substance, such as mass; intensive properties do not depend on the amount, such as temperature.

Question 2

A student measures the mass of a sample as $12.34\ \mathrm{g}$ and its volume as $4.56\ \mathrm{mL}$. What is the density of the sample, and how many significant figures should the answer have?

Accepted Answer

$2.71\ \mathrm{g/mL}$, 3 significant figures

Question 3

Which of the following best illustrates the law of conservation of mass in a chemical reaction?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 4

Which of the following is the correct electron configuration for a ground-state oxygen atom ($Z=8$)?

Accepted Answer

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

Question 5

A photon has a wavelength of $500\ \mathrm{nm}$. What is its energy in joules? $(h = 6.626 	imes 10^{-34}\ \mathrm{J\cdot s},\ c = 3.00 	imes 10^8\ \mathrm{m/s})$

Accepted Answer

$3.98 	imes 10^{-19}\ \mathrm{J}$

Question 6

Which of the following best explains why sodium metal reacts violently with water, but magnesium does not?

Accepted Answer

Sodium has a lower ionization energy than magnesium, making it more reactive.

Question 7

Which of the following molecules has a dipole moment?

Accepted Answer

$\mathrm{H_2O}$

Question 8

A sample of gas occupies $10.0\ \mathrm{L}$ at $2.00\ \mathrm{atm}$ and $300\ \mathrm{K}$. What volume will it occupy at $1.00\ \mathrm{atm}$ and $300\ \mathrm{K}$? (Assume ideal gas behavior.)

Accepted Answer

$20.0\ \mathrm{L}$

Question 9

Which of the following is the correct Lewis structure for the nitrate ion, $\mathrm{NO_3^-}$?

Accepted Answer

One N–O single bond and two N=O double bonds, with resonance among all three oxygens.

Question 10

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

Accepted Answer

The reactant that determines the maximum amount of product formed.

Question 11

Which of the following statements about strong and weak electrolytes is correct?

Accepted Answer

Strong electrolytes dissociate completely in water; weak electrolytes dissociate partially.

Question 12

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the pathway taken.

Question 13

Which of the following best describes the Pauli exclusion principle?

Accepted Answer

No two electrons in an atom can have the same set of four quantum numbers.

Question 14

A solution is prepared by dissolving $0.10\ \mathrm{mol}$ of $\mathrm{NaCl}$ in $1.0\ \mathrm{L}$ of water. Which statement is correct about the resulting solution?

Accepted Answer

It contains $0.10\ \mathrm{mol}$ of $\mathrm{Na^+}$ ions and $0.10\ \mathrm{mol}$ of $\mathrm{Cl^-}$ ions.

Question 15

Which of the following best explains why the atomic radius decreases across a period from left to right?

Accepted Answer

Increasing nuclear charge pulls electrons closer to the nucleus.

Question 16

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

Accepted Answer

$\mathrm{CH_2O}$

Question 17

Which of the following best describes the difference between sigma ($\sigma$) and pi ($\pi$) bonds?

Accepted Answer

$\sigma$ bonds result from head-on overlap of orbitals; $\pi$ bonds result from side-on overlap.

Question 18

A reaction has $\Delta H = -100\ \mathrm{kJ}$ and $\Delta S = +200\ \mathrm{J/K}$. At what temperature (in K) does the reaction become non-spontaneous? $(\Delta G = \Delta H - T\Delta S)$

Accepted Answer

$500\ \mathrm{K}$

Question 19

Which of the following best describes the kinetic-molecular theory of gases?

Accepted Answer

Gas particles are in constant, random motion and collisions are elastic.

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