First of all, scientific laws describe an existing phenomenon or the reason behind an existing phenomenon. It is a law, an already established fact that has been discussed, debated, and proven by great and experienced minds. Scientific laws have been proven right and factual over time, and it remains acceptable even in the days to come.
A scientific law can only be rendered obsolete by another law. Scientific laws are results of universally accepted scientific theories. Examples of scientific laws are Newton's laws of motion and Henry's law in thermodynamics. On the other hand, scientific theories are just statements that are postulated, trying to describe the reason behind the occurrence of a phenomenon. These are based on observations that have just been discovered, but still under investigations and tests. It tries to explain an existing fact also predicts new ones. Scientific theories, when proven and generally accepted, become scientific laws.