Q: What is the total energy required to heat 15.0 g of ethanol from 25.0°C to its boiling point (78.0°C) and then vaporize it? (Specific heat = 2.46 J/g°C, heat of vaporization = 841 J/g)

$$15.0 \times (78.0 - 25.0) \times 2.46 + 15.0 \times 841 = 14,600 J$$

Q: A volcano releases 175 g of steam at 100°C. How much total energy in kJ is released when the steam condenses and then freezes at 0°C? (Heat of vaporization = 2260 J/g, heat of fusion = 334 J/g, specific heat of water = 4.18 J/g°C)

$$175 \times 2260 + 175 \times 100 \times 4.18 + 175 \times 334 = 528 kJ$$

Q: If 50.0 g of steam at 100°C condenses, how much energy in kJ is released? (Heat of vaporization for water = 2260 J/g)

$$50.0 \times 2260 = 113,000 J$$ = $$113 kJ$$

Question 1

Which of the following pairs of atoms will form a nonpolar covalent bond based on their electronegativity values: C (2.5) and H (2.1), N (3.0) and O (3.5), Cl (3.0) and F (4.0), or Si (1.8) and Si (1.8)?

Accepted Answer

Si (1.8) and Si (1.8)

Question 2

A bond between Na (0.9) and Cl (3.0) is best classified as which type of bond? Calculate the electronegativity difference to support your answer.

Accepted Answer

Ionic; $$3.0 - 0.9 = 2.1$$

Question 3

Which statement best explains why the molecule CO$$_2 is $$nonpolar, even though it contains polar bonds?

Accepted Answer

The molecule has a linear shape and the bond dipoles cancel each other.

Question 4

Given the electronegativity values: P (2.1) and Cl (3.0), what is the bond type and the direction of the dipole?

Accepted Answer

Polar covalent; dipole points from P to Cl

Question 5

Which intermolecular force is primarily responsible for the high boiling point of water?

Accepted Answer

Hydrogen bonding

Question 6

A sample of 32.0 g of ice at 0°C is melted. How much energy in joules is required for this process? (Heat of fusion for water = 334 J/g)

Accepted Answer

$$32.0 	imes 334 = 10,700 J$$

Question 7

Which molecule is polar due to its shape and bond dipoles not cancelling: CH$$_4$$, CO$$_2$$, NH$$_3$$, or CCl$$_4$$?

Accepted Answer

NH$$_3$$

Question 8

What is the total energy required to heat 15.0 g of ethanol from 25.0°C to its boiling point (78.0°C) and then vaporize it? (Specific heat = 2.46 J/g°C, heat of vaporization = 841 J/g)

Accepted Answer

$$15.0 	imes (78.0 - 25.0) 	imes 2.46 + 15.0 	imes 841 = 14,600 J$$

Question 9

Which of the following best describes the process of sublimation?

Accepted Answer

A solid changes directly to a gas with heat added.

Question 10

A volcano releases 175 g of steam at 100°C. How much total energy in kJ is released when the steam condenses and then freezes at 0°C? (Heat of vaporization = 2260 J/g, heat of fusion = 334 J/g, specific heat of water = 4.18 J/g°C)

Accepted Answer

$$175 	imes 2260 + 175 	imes 100 	imes 4.18 + 175 	imes 334 = 528 kJ$$

Question 11

Which of the following molecules will have only dispersion forces as the main intermolecular interaction?

Accepted Answer

N$$_2$$

Question 12

What is the electronegativity difference and bond type for a bond between Br (2.8) and Cl (3.0)?

Accepted Answer

Difference: $$3.0 - 2.8 = 0.2$$; Nonpolar covalent

Question 13

Which of the following is NOT a factor in determining if a molecule is polar?

Accepted Answer

Atomic mass of the central atom

Question 14

Which of the following best describes the direction of the dipole in a polar covalent bond?

Accepted Answer

From the less electronegative atom to the more electronegative atom

Question 15

Which of the following molecules is nonpolar due to its symmetrical arrangement of polar bonds?

Accepted Answer

CCl$$_4$$

Question 16

What is the main reason ionic compounds have higher melting points than molecular compounds?

Accepted Answer

Ionic compounds have stronger attractive forces between ions.

Question 17

Which process occurs at the boiling point of a liquid when heat is added?

Accepted Answer

Vaporization

Question 18

Which of the following is the strongest type of intermolecular force found in proteins that allows them to maintain a specific three-dimensional shape?

Accepted Answer

Hydrogen bonds

Question 19

If 50.0 g of steam at 100°C condenses, how much energy in kJ is released? (Heat of vaporization for water = 2260 J/g)

Accepted Answer

$$50.0 	imes 2260 = 113,000 J$$ = $$113 kJ$$

Electronegativity, Bond Polarity, and Molecular Polarity: Study Notes for Introductory Chemistry

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