Chapter 3

Thermal Energy

Kinetic energy due to the random motion of atoms and molecules; energy in its most random form.

Molarity

A common measure of solute concentration, referring to the number of moles of solute per liter of solution.

Polar Covalent Bond

A covalent bond between atoms that differ in electrognegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and he other atom slightly positive.

Solution

A liquid that is a homogeneous mixture of two or more substances

Temperature

A measure in degrees of the average kinetic energy (thermal energy) of the atoms and molecules in a body of matter.

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.

pH

A measure of hydrogen ion concentration equal to -log[H+] and ranging in value from 0 to 14.

Polar Molecule

A molecule with an uneven distribution of charges in different regions of the molecule.

Hydrogen Ion

A single proton with a charge of 1 +. The dissociation of a water molecule (H2O) leads to the generation of a hydroxide ion (OH-) and a hydrogen ion (H+); in water, H+ is not found alone but associates with a water molecule to form a hydronium ion .

Aqueous Solution

A solution in which water is the solvent.

Buffer

A solution that contains a weak acid and its corresponding base. A buffer minimizes changes in pH when acids or bases are added to the solution.

Acid

A substance that increases the hydrogen ion concentration of a solution

Solute

A substance that is dissolved in a solution.

Base

A substance that reduces the hydrogen ion concentration of a solution.

Kilocalorie

A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1 degree celsious

Joule

A unit of energy; 1 J = 0.239 cal; 1 cal = 4.184J

Hydronium Ion

A water molecule that has an extra proton bound to itl H3O+, commonly represented as H+

Hydroxide Ion

A water molecule that has lost a proton; OH-

If the molecular mass of a carbon atom is 12, the mass of a hydrogen atom is 1, and the mass of an oxygen atom is 16 daltons, how many molecules does one mole of table sugar (sucrose; C12H22O11) contain? See Concept 3.2 (Page 49) A. 6.02 x 10E23 C. 45 D. 6.02 x 1023/342 E. (6.02 x 1023)(342) F. 342

A. 6.02 x 10E23 In fact, this is the number of molecules in one mole of any substance.

Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _____. See Concept 3.1 (Page 45) A. hydrogen bond B. sionic bonds C. nonpolar covalent bonds D. polar covalent bonds E. Van der Waals interactions

A. hydrogen bond The polarity of a water molecule allows the oxygen of one water molecule to bond weakly to the hydrogen of another water molecule.

Hydrophobic substances such as vegetable oil are _____. A. nonpolar substances that repel water molecules B. nonpolar substances that have an attraction for water molecules C. polar substances that repel water molecules D. polar substances that have an affinity for water

A. nonpolar substances that repel water molecules

A pH of 6 is how many times more acidic than a pH of 9? See Concept 3.3 (Page 51) A. 3 B. 30 C. 100 D. 300 E. 1,000

E. 1,000 A pH of 6 is 10 times more acidic than 7, which is 10 times more acidic than 8, which is 10 times more acidic than 9. 10 x 10 x 10 = 1,000.

Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____. See Concept 3.2 (Page 46) A. lower density in the solid phase B. buffering activity C. ability to form colloids D. cohesion E. high specific heat

E. high specific heat Water has a high specific heat, meaning that a relatively large amount of heat must be added or removed in order to get the temperature of the water to change significantly.

Hydrophilic

Having an affinity for water.

Hydrophobic

Having no affinity for water; tending to coalesce and form droplet in water.

Adhesion

The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.

Solvent

The dissolving agent of a solution. Water is the most versatile solvent known.

Calorie

The amount of heat energy required to raise the temperature of 1 g of water by 1 deg celsius; also the amount of heat energy that 1 g of water releases when it cools by 1 degree celsius. The Calorie, usually used to indicate the energy content of food, is a kilocalorie.

Specific Heat

The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1 deg celsius

All of the following statements help to explain why water molecules form hydrogen bonds except: A. The electrons spend more time around the oxygen atom because oxygen is more electronegative than hydrogen. B. Attractions form between opposite partial charges. C. Water is an electronegative molecule. D. There is a partial positive charge on each hydrogen atom and two partial negative charges on the oxygen atom in a water molecule.

C. Water is an electronegative molecule. Elements, not molecules, can be electronegative. When a hydrogen atom is covalently bonded to an electronegative atom such as oxygen in water, the hydrogen atom has a partial positive charge and the oxygen atom has a partial negative charge, making water a polar molecule. The hydrogen atom is attracted to a different electronegative atom nearby. This attraction between the partial positive charge on the hydrogen atom and the partial negative charge on an electronegative atom is called a hydrogen bond.

An acid is a substance that _____. See Concept 3.3 (Page 51) A. reduces the hydrogen ion concentration of a solution B. forms covalent bonds with other substances C. is a versatile solvent D. increases the hydrogen ion concentration of an aqueous solution E. contains hydrogen

D. increases the hydrogen ion concentration of an aqueous solution As an acid dissociates, it donates a hydrogen ion to the solution.

The amount of energy that must be absorbed or lost to raise or lower the temperature of 1 g of liquid water by 1°C _____. See Concept 3.2 (Page 46) A. is 1,000 joules B. is 1 kilocalorie C. is 1,000 kilocalories D. is 1 calorie E. depends on the initial temperature of the water sample F. is 1,000 calories

D. is 1 calorie The specific heat of liquid water is 1 cal/g/°C.

Electronegativity is A. the negative charge surrounding the nucleus of an atom. B. the number of electrons in the outermost electron shell. C. the repulsion of electrons in one atom for electrons in another atom. D. the attraction of an atom for the electrons in a covalent bond.

D. the attraction of an atom for the electrons in a covalent bond. If you had trouble with this question, review the following material: Atoms in a molecule attract shared bonding electrons to varying degrees, depending on the element. The more electronegative an atom is, the more strongly it pulls shared electrons toward itself.

The partial negative charge in a molecule of water occurs because _____. A. the oxygen atom has two pairs of electrons in its valence shell that are not neutralized by hydrogen atoms B. one of the hydrogen atoms donates an electron to the oxygen atom C. the oxygen atom donates an electron to each of the hydrogen atoms D. the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus

D. the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus

A polar covalent bond between two atoms results from A. whether the bond is single or not. B. the presence of two ions close to each other. C. the shape of the molecule that has the bond. D. two atoms that do not have similar electronegativities.

D. two atoms that do not have similar electronegativities. When an atom is bonded to a more electronegative atom, the electrons of the bond are not shared equally. This type of bond is called a polar covalent bond. Such bonds vary in their polarity, depending on the relative electronegativity of the two atoms.

Kinetic Energy

The energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter.

Cohesion

The linking together of like molecules, often by hydrogen bonds.

Mole (mol)

The number of grams of a substance that equals its molecular or atomic mass in daltons; a mole contains Avodgadro's number of the molecules or atoms in question.

Ocean Acidification

The process by which the pH of the ocean is lowered (made more acidic) when excess CO2 dissolves in seawater and forms carbonic acid (H2CO3)

Evaporative Cooling

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state.

Heat of Vaporization

The quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

Hydration Shell

The sphere of water molecules around a dissolved ion.

Molecular Mass

The sum of the masses of all the atoms in a molecule; sometimes called molecular weight

Heat

Thermal energy in transfer from one body of matter to another.