<em><u>A closed system is a physical system that does not allow transfer of matter in or out of the system, though, in different contexts, such as physics, chemistry or engineering, the transfer of energy is or is not allowed.</u></em>
HCN - Hydrogen cyanide The conjugate acid of CN- is HCN. HCN stands for hydrogen cyanide. The conjugate acids are a combination of a strong acid and a low base.