Q: A photon has a frequency of $$6.0 \times 10$$^{14}$$\ \mathrm{Hz}. $$What is its energy in joules? (Planck's constant $$h = 6.626 \times 10$$^{-34}$$\ \mathrm{J\cdot s})$$

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

Question 1

Which of the following statements best distinguishes between a physical and a chemical change? Consider the example of ice melting and iron rusting.

Accepted Answer

Ice melting is a physical change because the molecular composition remains the same, while iron rusting is a chemical change because new substances are formed.

Question 2

A sample of an unknown element has two naturally occurring isotopes: $$^{63}\mathrm{X} ($$abundance 69.2%, mass 62.93 amu) and $$^{65}\mathrm{X} ($$abundance 30.8%, mass 64.93 amu). What is the average atomic mass of element X?

Accepted Answer

$$63.55\ \mathrm{amu}$$

Question 3

Which of the following best describes the difference between extensive and intensive properties? Choose the correct example pair.

Accepted Answer

Volume is extensive and temperature is intensive; volume depends on amount, but temperature does not.

Question 4

A chemist needs to convert $$25.0\ ^\circ\mathrm{C} to $$Kelvin. Which equation and answer should they use?

Accepted Answer

$$K = ^\circ\mathrm{C} + 273.15$$; $$25.0 + 273.15 = 298.2\ \mathrm{K}$$

Question 5

Which of the following correctly describes the relationship between wavelength ($$\lambda$$), frequency ($$
u$$), and the speed of light ($$c) $$for electromagnetic radiation?

Accepted Answer

$$c = \lambda 
u$$

Question 6

A photon has a frequency of $$6.0 	imes 10$$^{14}$$\ \mathrm{Hz}. $$What is its energy in joules? (Planck's constant $$h = 6.626 	imes 10$$^{-34}$$\ \mathrm{J\cdot s})$$

Accepted Answer

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

Question 7

Which of the following elements is a metalloid and is located in period 3 of the periodic table?

Accepted Answer

Silicon (Si)

Question 8

Which of the following is the correct electron configuration for the $$\mathrm{O}^{2-}$$ ion?

Accepted Answer

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

Question 9

Which of the following statements about the photoelectric effect is correct?

Accepted Answer

Electrons are emitted from a metal surface only if the incident light has a frequency above a certain threshold, regardless of intensity.

Question 10

Which of the following best explains why the first ionization energy generally increases across a period from left to right?

Accepted Answer

Effective nuclear charge ($$Z_{\mathrm{eff}}) $$increases, pulling electrons closer to the nucleus and requiring more energy to remove an electron.

Question 11

A sample contains $$0.250\ \mathrm{mol} of$$ $$\mathrm{NaCl}. $$How many formula units of $$\mathrm{NaCl}$$ are present? (Avogadro's number $$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$1.51 	imes 10$$^{23}$$

Question 12

Which of the following quantum number sets is NOT allowed for an electron in an atom?

Accepted Answer

$$n=2,\ l=2,\ m_l=0$$

Question 13

Which of the following best describes the de Broglie wavelength of a particle and its dependence on mass and velocity?

Accepted Answer

The de Broglie wavelength is inversely proportional to both mass and velocity: $$\lambda = \dfrac{h}{mv}$$

Question 14

A hydrogen atom electron transitions from $$n=4 to$$ $$n=2. $$Which region of the electromagnetic spectrum is the photon emitted in, and why?

Accepted Answer

Visible region, because Balmer series transitions end at $$n=2$$ and emit visible light.

Question 15

Which of the following is a correct application of Coulomb’s Law to explain periodic trends in atomic size?

Accepted Answer

As effective nuclear charge increases across a period, the attraction between the nucleus and valence electrons increases, causing atomic size to decrease.

Question 16

Which of the following elements exists as a diatomic molecule under standard conditions?

Accepted Answer

Nitrogen ($$\mathrm{N}_2)$$

Question 17

A student measures the mass of a sample as $$12.345\ \mathrm{g}$$ and the volume as $$6.7\ \mathrm{mL}. $$What is the density, reported with the correct number of significant figures?

Accepted Answer

$$1.8\ \mathrm{g/mL}$$

Question 18

Which of the following best describes the Pauli Exclusion Principle?

Accepted Answer

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

Question 19

A sample of gas has a density of $$1.25\ \mathrm{g/L} at$$ $$STP. $$What is the molar mass of the gas? ($$STP: 1\ \mathrm{atm},\ 273.15\ \mathrm{K},\ 22.4\ \mathrm{L/mol})$$

Accepted Answer

$$28.0\ \mathrm{g/mol}$$

General Chemistry I: Matter, Energy, and Atomic Structure – Exam 1 Study Guide

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