A region of space within the universe. Systems are considered in thermodynamic or other studies to determine how a change in the environment (e.g., temperature changes, pressure changes, etc.) will affect the system. Systems may be closed by encapsulating in noble metals, placing a liquid in a sealed beaker, etc. A “closed system” is affected only by receiving energy from or giving energy to the outside environment. An “open system” differs from a closed system by an exchange of matter, in addition to energy. An “isolated system” receives neither matter nor energy across the boundary.