Scientific laws are similar to scientific theories in that they are principles that can be used to predict the behavior of the natural world. Both scientific laws and scientific theories are typically well-supported by observations and/or experimental evidence. Scientific laws usually refer to rules for how nature will behave under certain conditions, while scientific theories are more overarching explanations of how nature works and why it exhibits certain characteristics.
Around the year 1800, Jacques Charles and other scientists were working with gases to, among other reasons, improve the design of the hot air balloon. These scientists found, after many, many tests, that patterns and regularities existed in the behavior of gas. If the temperature of the gas increased, the volume of the gas increased. This is known as a natural law. Natural laws describe the patterns we see in large amounts of data but do not describe why the patterns exist.
A common misconception is that scientific theories are rudimentary ideas that will eventually graduate into scientific laws when enough data and evidence has been accumulated. A theory does not change into a scientific law with the accumulation of new or better evidence. Remember, theories are explanations while laws are patterns we see in large amounts of data, frequently written as an equation. A theory will always remain a theory, a law will always remain a law.
http://www.ck12.org/book/Introductory-Chemistry/r1/section/1.1/Introduction-to-Chemistry-and-The-Nature-of-Science-%253A%253Aof%253A%253A-Introductory-Chemistry/