Chapter 3: Water and Life
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35 terms
Terms | Definitions |
|---|---|
 polar covalent bond | A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive. |
| polar molecule | A molecule (such as water) with an uneven distribution of charges in different regions of the molecule. |
| cohesion | The linking together of like molecules, often by hydrogen bonds. |
| adhesion | The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds. |
| 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. |
| kinetic energy | The energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter. |
| heat | The total amount of kinetic energy due to the random motion of atoms or molecules in a body of matter; also called thermal energy. Heat is energy in its most random form. |
| temperature | A measure of the intensity of heat in degrees, reflecting the average kinetic energy of the molecules. |
| Celsius scale | A temperature scale (°C) equal to 5/9(°F - 32) that measures the freezing point of water at 0 °C and the boiling point of water at 100 °C. |
| calorie (cal) | The amount of heat energy required to raise the temperature of 1 g of water by 1 °C; also the amount of heat energy that 1 g of water releases when it cools by 1 °C. The Calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie. |
| kilocalorie (kcal) | A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1 °C. |
| joule (J) | A unit of energy: 1 J = 0.239 cal; 1 cal = 4.184 J. |
| specific heat | The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1 °C. |
| 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. |
| 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. |
| solution | A liquid that is a homogeneous mixture of two or more substances. |
| solvent | The dissolving agent of a solution. Water is the most versatile solvent known. |
| solute | A substance that is dissolved in a solution. |
| aqueous solution | A solution in which water is the solvent. |
| hydration shell | The sphere of water molecules around a dissolved ion. |
| hydrophilic | Having an affinity for water. |
| colloid | A mixture made up of a liquid and particles that (because of their large size) remain suspended rather than dissolved in that liquid. |
| hydrophobic | Having no affinity for water; tending to coalesce and form droplets in water. |
| molecular mass | The sum of the masses of all the atoms in a molecule; sometimes called molecular weight. |
| mole (mol) | The number of grams of a substance that equals its molecular weight in daltons and contains Avogadro's number of molecules. |
| molarity | A common measure of solute concentration, referring to the number of moles of solute per liter of solution. |
| 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. |
| hydroxide ion | A water molecule that has lost a proton; OH⁻. |
| hydronium ion | A water molecule that has an extra proton bound to it; H₃O⁺, commonly represented as H⁺. |
| acid | A substance that increases the hydrogen ion concentration of a solution. |
| base | A substance that reduces the hydrogen ion concentration of a solution. |
| pH | A measure of hydrogen ion concentration equal to -log [H⁺] and ranging in value from 0 to 14. |
| buffer | A solution that contains a weak acid and its corresponding base. A bugger minimizes changes in pH when acids or bases are added to the solution. |
| ocean acidification | Decreasing pH of ocean waters due to absorption of excess atmospheric CO₂ from the burning of fossil fuels. |
| acid precipitation | Rain, snow, or fog that is more acidic than pH 5.2. |
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