What is the best way to prepare for an organic chemistry exam?
If you have 1 or 2 days before an exam, the best way to study is to first define the scope of what the exam covers and do all of the practice problems from homeworks, problems sets, and labs from the course. Not surprisingly, what shows up on the homework and lab will oftentimes show up again on the exams. If you're short on time, it's much more effective to cram by doing than to cram by memorizing.
What is the difference between a physical and chemical change?
While both physical and chemical changes involve the breaking and forming of bonds, physical changes do alter the identity of the substance and is a reversible change, such as the melting of ice to form water. Chemical changes, on the other hand, involve the breaking and forming of chemical bonds (ionic, covalent) to form entirely new substances, such as the combustion of methane with oxygen to form carbon dioxide and water.
What is a chemical reaction and why do we need to balance the coefficients in a chemical equation?
A chemical reaction is a process where the bonds connecting the atoms of the reactants are broken and rearranged to form new bonds that make up atoms in the products. The reason we need to balance chemical equations is to follow the conservation of matter, which tells us that no atoms can be created or destroyed during a chemical reaction, meaning the number of atoms of each element we start with in the reactants must equal the number of atoms of elements we end up with in the products.