Week 4 of the Science Enrichment Program covered physical chemistry, the science that aims to develop a fundamental understanding at the molecular and atomic level of how materials behave and how chemical reactions occur, knowledge that is relevant in nearly every area of chemistry. The students learned the importance of physical chemistry in understanding the phases of matter, combustion, protein structure, and chemical energy. The students also learned about the advanced tools physical chemists use to develop this understanding, such as supercomputers, electron microscopes, and lasers. For the hands-on activities, the students investigated the strength of the molecular interactions between water molecules, e.g. hydrogen bonding, as compared to other liquids. This investigation was conducted by counting drops of liquid held on top of a penny. Groups of students also constructed fuel cell cars, powered by a promising clean energy source of the future. This activity demonstrated how fuel cells combine hydrogen and oxygen gasses to generate water and energy to power a vehicle. To fill up the "gas" tank, the fuel cell car first split water into the necessary gasses via electrolysis using power obtained from a solar panel.