Q: Which of the following equations correctly represents the conservation of mass in a chemical reaction?

$$\sum m_{\text{reactants}} = \sum m_{\text{products}}$$

Q: A patient receives a medication that undergoes the following reaction in the body: $$C_6H_{12}O_6$ + 6O_2 \rightarrow 6CO_2 + 6H_2O. If $$the patient metabolizes 10 grams of glucose ($$C_6H_{12}O_6$), how many grams of CO_2$ are produced? (Molar masses: C_6H$$_{12}$$O_6 = 180$ g/mol, CO_2$ = 44 g/$$mol)

10 g $$C_6H_{12}O_6$ × $$\frac{1\ \text{mol}}{180\ \text{g}}$$ × $$\frac{6\ \text{mol}\ $$CO_2$$}{1\ \text{mol}\ C_6H_{12}$$O_6$$}$$ × $$\frac{44\ \text{g}}{1\ \text{mol}}$$ = 14.7 g CO_2$

Q: Consider the following reaction: $$H_2(g$$) + $$Cl_2(g$$) \rightarrow 2HCl(g)$$. Given the bond energies: H-H = 436$ kJ/mol, Cl-Cl = 243$ kJ/mol, H-Cl = 431$ kJ/mol. What is the enthalpy change ($$\Delta H$$) for the reaction?

$$\Delta H = [436 + 243] - [2 \times 431] = -183 kJ$$

Question 1

Which of the following best describes the concept of formal charge in a covalent molecule?

Accepted Answer

The charge assigned to an atom assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity.

Question 2

Given the Lewis structure for the nitrate ion ($$NO_3$$^-$$), what is the formal charge on each oxygen atom if the structure is drawn with one double bond and two single bonds?

Accepted Answer

One oxygen has a formal charge of 0, and the other two have a formal charge of $$-1.$$

Question 3

Which of the following equations correctly represents the conservation of mass in a chemical reaction?

Accepted Answer

$$\sum m_{	ext{reactants}} = \sum m_{	ext{products}}$$

Question 4

A patient receives a medication that undergoes the following reaction in the body: $$C_6H_{12}O_6$ + 6O_2 \rightarrow 6CO_2 + 6H_2O. If $$the patient metabolizes 10 grams of glucose ($$C_6H_{12}O_6$), how many grams of CO_2$ are produced? (Molar masses: C_6H$$_{12}$$O_6 = 180$ g/mol, CO_2$ = 44 g/$$mol)

Accepted Answer

10 g $$C_6H_{12}O_6$ × $$\frac{1\ 	ext{mol}}{180\ 	ext{g}}$$ × $$\frac{6\ 	ext{mol}\ $$CO_2$$}{1\ 	ext{mol}\ C_6H_{12}$$O_6$$}$$ × $$\frac{44\ 	ext{g}}{1\ 	ext{mol}}$$ = 14.7 g CO_2$

Question 5

Which of the following statements about bond energies is correct?

Accepted Answer

Breaking a chemical bond always requires energy input.

Question 6

Consider the following reaction: $$H_2(g$$) + $$Cl_2(g$$) \rightarrow 2HCl(g)$$. Given the bond energies: H-H = 436$ kJ/mol, Cl-Cl = 243$ kJ/mol, H-Cl = 431$ kJ/mol. What is the enthalpy change ($$\Delta H$$) for the reaction?

Accepted Answer

$$\Delta H = [436 + 243] - [2 	imes 431] = -183 kJ$$

Question 7

Which of the following best explains why $$O_2 is a $$diatomic molecule under standard conditions?

Accepted Answer

Each oxygen atom achieves a stable octet by sharing two electrons with another oxygen atom, forming a double bond.

Question 8

A student is asked to draw the Lewis structure for $$CO_2. $$Which of the following is the correct structure and formal charge assignment?

Accepted Answer

O=C=O, with all atoms having a formal charge of 0.

Question 9

Which of the following is a correct application of the law of conservation of energy in a chemical reaction?

Accepted Answer

The total energy of the system and surroundings remains constant during a chemical reaction.

Question 10

In a real-world scenario, why is it important to consider bond energies when designing new pharmaceuticals?

Accepted Answer

Bond energies determine the stability and reactivity of molecules, affecting how drugs interact with biological targets.

Question 11

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of electrons between two nonmetal atoms.

Question 12

A chemical reaction in a car engine releases 500 kJ of energy as heat. According to the law of conservation of energy, what happens to this energy?

Accepted Answer

It is transferred to the surroundings, increasing the temperature of the engine and air.

Question 13

Which of the following is the correct formula for calculating the formal charge ($$FC) on an $$atom in a molecule?

Accepted Answer

$$FC = 	ext{valence electrons} - (	ext{nonbonding electrons} + \frac{1}{2} 	imes 	ext{bonding electrons})$$

Question 14

Which of the following best explains why the total mass of reactants equals the total mass of products in a chemical reaction?

Accepted Answer

Atoms are neither created nor destroyed in a chemical reaction.

Question 15

A chemist is analyzing the combustion of propane: $$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O. If 44 g of$$ $$CO_2$$ are produced, how many grams of $$C_3H_8$$ were combusted? (Molar masses: $$C_3H_8 = 44 g/$$mol, $$CO_2 = 44$ g/mol)

Accepted Answer

44 g $$CO_2$$ × $$\frac{1\ 	ext{mol}}{44\ 	ext{g}}$$ × $$\frac{1\ 	ext{mol}\ C_3H_8}{3\ 	ext{mol}\ CO_2$}$$ × $$44\ 	ext{g} = 14.7 g$$ $$C_3H_8$$

Question 16

Which of the following is a real-life example of the conservation of mass?

Accepted Answer

When wood burns in a closed container, the total mass of the container and its contents remains the same before and after combustion.

Question 17

Which of the following statements about covalent bonding is correct?

Accepted Answer

Covalent bonds involve the sharing of electron pairs between atoms.

Question 18

A molecule of $$NH_3 ($$ammonia) has which of the following features?

Accepted Answer

Three single covalent bonds and one lone pair on nitrogen.

Question 19

Which of the following best describes the energy changes when a bond is formed between two atoms?

Accepted Answer

Energy is released as the atoms achieve a more stable, lower-energy state.

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