Chapter 1 - Chemistry, "the central science"

endothermic change

a chemical change that absorbs energy. for example: we must heat water to covert it to steam -- this is endothermic change.

exothermic change

a chemical change that releases heat energy for example: wood burning on a campfire is an example of exothermic change

scientific method

a cyclical process of making observations, formulating new ideas, and then testing those ideas through experiments.

scientific law

a statement that describes observations that are true in widely varying circumstances. scientific laws often describe mathematical relationships. however, they do not explain why something occurs; they only observe that it occurs. for example: consider the law of gravity -- this law describes observations and phenomenon that consistently occur. scientists use the law of gravity mathematically, to calculate the weight of a building or the trajectory of a rocket. this law predicts what will happen, but it does not explain why it happens.

hypothesis

a tentative explanation that has not been tested. to test a hypothesis, scientists devise experiments. The results of experiments provide support for or against a hypothesis, and they lead scientists to embrace, refine, or discard their ideas. the observations that scientists make from experiments often lead to new hypotheses, which in turn lead to new experiments.

heat energy

a type of kinetic energy heat energy involves the kinetic energy of particles within a substance. when a substance is heated, the particles within the substance vibrate or move more and more quickly. for example, if a stove is hot, the particles on the hot surface vibrate more rapidly than if the stove is cold. on the macroscopic level, the stove doesn't have kinetic energy (it is sitting still) -- but on an atomic level, the particles on the surface of the stove are moving rapidly.

classify the phrases pertaining to pure substances and mixtures as either true or false: a.) homogeneous mixtures have uniform properties throughout. b.) components of a homogeneous mixture are visibly distinct. c.) heterogeneous mixtures contain more than one part, and each part has its own properties. d.) the components of homogeneous and heterogeneous mixtures cannot be separated. e.) pure substances only contain one type of substance and nothing else.

a.) true b.) false c.) true d.) false e.) true

theory

an idea that has been tested and refined; also a way of thinking about a particular topic. this term can also have a broader meaning: sometimes it is used to mean a paradigm—a way of thinking about a particular topic. when scientists talk about a theory, they mean an idea that is supported by evidence, or even a way of thinking about the world around us.

matter

anything that has mass and takes up volume

physical changes

changes that occur without altering the identity of the substance. for example, we can take an iron bar, melt it, pour it into a mold, and let it cool, solidifying into a new shape. we have altered the shape and phase of the iron, but it is still composed of iron, and so each of these changes is a physical change.

chemical change

changes that produce new substances; also called chemical reactions. in some chemical changes, elements combine to form compounds. for example, when heated, zinc and sulfur combine to form a new compound, zinc sulfide. in other chemical changes, compounds break apart to produce elemental substances or rearrange to form new compounds. for example, methane gas can react to oxygen gas to produce two new compounds, carbon dioxide and water. the key idea is that a chemical change always involves the formation of a different substance.

extensive physical properties

depend on the amount of matter present and include mass, length, and volume

states of matter: gas

do not have definite shape or volume -- gases fill any container they occupy. particles in a gas move freely with very little interactions.

potential energy

energy that is stored

atoms

fundamental units of matter; a tiny unit of matter scientists use tiny spheres or by using one- or two-letter symbols or by combining the two to represent atoms.

molecules

groups of atoms that are held tightly together -- formed by groups of atoms via compounds. the atoms behave as a single unit. for example, a water molecule contains two hydrogen atoms and one oxygen atom. some elements also exists as molecules -- in hydrogen, nitrogen, and oxygen, the atoms of the element pair together to form diatomic ("two-atom") molecules.

states of matter: liquids

have a definite volume, but no definite shape -- liquids adopt the shape of their container. particles in liquids are close together but move freely past eachother.

states of matter: solid

have both definite shape and definite volume particles in a solid are held in fixed positions.

high energy and stable

high energy -- either kinetic or potential; can bring about change stable -- has less energy and less likely to react

hypothesis, theory, and law example

hypothesis: -- an untested explanation -- a botanist guesses, but has not verified, why plants with one red-flowered and one white flowered parent have pink flowers. theory: -- an explanation that has been tested and verified. -- scientists, after many experiments, explain how the temperature of a gas depends on the energy of its molecules. law: -- a description that predicts what happens, but does not explain how.

states of matter: phases

if we heat a substance, it can transform a solid to a liquid (melting) -- or from a liquid to gas (vaporization). if we cool it, the reverse occurs: gas changes to liquid (condensation), and the liquid changes to a solid (freezing) the states of matter offer an important message: the behavior of any substance is determined by the arrangement of particles that compose the substance.

heterogeneous mixture

mixtures in which the components are not evenly blended throughout. for example, sand and water, gravel, and chocolate-chip cookie dough are heterogeneous mixtures. they each have regions where one component is present in far greater proportion.

homogenous mixture

mixtures whose components are evenly blended throughout. metal alloys, a cup of coffee, and the air around us are all homogeneous mixtures.

a theory is another word for a(n) _______

model

intensive physical properties

properties that do not depend on the amount of matter present

chemical properties

properties we cannot measure without changing the identity of a substance. for example, flammability is a chemical property. if we want to determine if something is flammable, we must burn it. if it burns, it is no longer the original substance. when a substance changes into something different, it has undergone a chemical change.

compounds

pure substances composed of more than one element in a fixed ratio. for example, water is made up of two parts hydrogen and one part oxygen. if the ratio of hydrogen and oxygen changes at all from 2:1, it is no longer water, but some other substance.

a homogeneous mixture is also called a _______

solution

pure substances

substances composed of only one element or only one compound.

mixtures

substances containing more than one type of substance. for example, brass and bronze are both mixtures of metals, known as alloys. brass is a mixture of the pure substances copper and zinc, while bronze is a mixture of the pure substances copper and tin. in these mixtures, the ratio of copper or other materials is not fixed -- it may be altered to affect properties of the alloy, such as hardness and color.

energy

the ability to do work energy takes two forms: kinetic and potential

structure

the arrangement of simple units within a substance. in chemistry, structure refers to both the composition and arrangement of simple units within a substance.

composition

the components that make up material

kinetic energy

the energy of motion -- the faster an object is moving, the greater kinetic energy it has.

physical properties

the properties of a substance that can be measured without changing the identity of a substance for example, we can measure color, temperature, mass, volume, shape, hardness, flexibility, and a host of other factors without changing the composition of the substance.

element

the simplest form of matter; made up of only one type of atom. common elements include gold, silver, iron, oxygen, and nitrogen. each element is composed of a unique type of atom -- for example, gold contains only gold atoms, silver only contains silver atoms.

chemistry

the study of matter and its changes

states of matter

the three phases of matter: solid, liquid, and gas distinguished by properties visible on a macroscopic level (visible to the naked eye)