Q: Which of the following is the correct formula for calculating the energy change ($$\Delta H) in a $$chemical reaction?

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

Question 1

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound is made of two or more elements chemically bonded, while a mixture contains substances physically combined without chemical bonds.

Question 2

Which of the following is the correct electron configuration for a neutral oxygen atom?

Accepted Answer

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

Question 3

A student mixes sand and salt in water. After stirring, the sand settles at the bottom, while the salt dissolves. Which type of mixture is formed?

Accepted Answer

A suspension

Question 4

Which of the following best explains why water is a polar molecule?

Accepted Answer

Water has a bent molecular shape and an uneven distribution of electrons due to the difference in electronegativity between hydrogen and oxygen.

Question 5

Which of the following is the correct balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 6

A solution has a $$[H^+]$$ concentration of $$1 	imes 10$$^{-4}$$\ 	ext{M}. $$What is the pH of the solution?

Accepted Answer

$$4$$

Question 7

Which statement about atomic structure is correct?

Accepted Answer

Protons and neutrons are found in the nucleus, while electrons are found in orbitals around the nucleus.

Question 8

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

Accepted Answer

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

Question 9

A sample of gas occupies $$2.0\ 	ext{L} at$$ $$1.0\ 	ext{atm}$$ pressure. If the pressure is increased to $$2.0\ 	ext{atm} at $$constant temperature, what is the new volume?

Accepted Answer

$$1.0\ 	ext{L}$$

Question 10

Which of the following is the correct Lewis structure for $$CO_2$$?

Accepted Answer

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

Question 11

Which of the following is NOT a property of acids?

Accepted Answer

They turn litmus paper blue.

Question 12

Which of the following best describes a colloid?

Accepted Answer

A mixture where particles are intermediate in size and do not settle out upon standing.

Question 13

Which of the following elements is most likely to form a $$2^+$$ cation?

Accepted Answer

Magnesium ($$Mg)$$

Question 14

Which of the following is the correct formula for calculating the energy change ($$\Delta H) in a $$chemical reaction?

Accepted Answer

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

Question 15

A solution is prepared by dissolving $$5.0\ 	ext{g} of$$ $$NaCl in $$enough water to make $$250\ 	ext{mL} of $$solution. What is the molarity of the solution? ($$M_{NaCl} = 58.44\ 	ext{g/mol})$$

Accepted Answer

$$0.34\ 	ext{M}$$

Question 16

Which of the following best describes the VSEPR theory?

Accepted Answer

Electron pairs around a central atom arrange themselves to minimize repulsion.

Question 17

Which of the following is a correct statement about isotopes?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 18

Which of the following is the correct formula for calculating the molar volume of a gas at STP?

Accepted Answer

$$22.4\ 	ext{L}$$ per $$1\ 	ext{mol}$$

Question 19

A chemical reaction absorbs heat from the surroundings. Which term best describes this process?

Accepted Answer

Endothermic

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