Chemistry chapter 1

Chemistry

Can be defined as the science that deals with the materials of the universe and the changes that these materials undergo. 

Scientific method

A process of studying natural phenomena that involves making observations, forming laws and theories, and testing theories by experimentation.

1. Recognize the problem clearly/ make an observation. It can be a qualitative observation or a quantitative observation, which is referred to as a measurement (discussed in Chapter 2).

2. Formulate hypotheses. A hypothesis is a possible explanation for the observation.

3. Experiment to test hypothesis.

To explain behaviors of nature, we repeat these steps many times and accumulate knowledge to know what’s going on.

Theory

A theory is an interpretation- a possible explanation of why nature behaves in a particular way. Once we have our hypotheses, we assemble them into a theory/model.

Observtaion applying to manny different systems

For example, studies of chemical changes have shown that the total mass of the materials involved is the same before and after the change. We often formulate such generally observed behavior into a statement called a natural law (statement that expresses generally observed behavior). The observation that the total mass of materials is not affected by a chemical change in those materials is called the law of conservation mass.

A law is a summary of observed (measurable) behavior.

Observation vs theory

Observation- something that is witnessed or recorded

Theory- an interpretation/ a possible explanation of why nature behaves in a particular way

Natural law

A statement that expresses generally observed behavior.

Ex: the observation that the total mass of materials involved is the same before and after the chemical change is called the law of conservation of mass

law vs theory

Law- summary of observed behavior

Theory- explanation of behavior

Physical changes

Something that changes the physical properties of a substance, such as size, shape, or form.

1. Do not form a new substance

2. may change shape or size

3. May change state of matter

4. Can often be undone

Examples:

-changing the states of matter of water

-mixing sugar and water, and they can be separated

-making a mixture for a cake

Chemical change/reaction

A reaction that rearranges the particles of 2 or more substances to create at least one new substance.

1. Always form a new substance

2. May absorb or release heat

3. May change color, produce odor, create sound, release gas, or produce light

4. Usually cannot be undone

Examples:

-Putting a mixture in the oven to make a cake. The mixture will absorb heat, change color, and produce an odor. This change cannot be undone.

-Metal rusting

-Fruit ripening