![]() ![]() It is the work associated with a change in volume that occurs against a resisting external pressure. The work performed in this demonstration is an example of pressure-volume work. The balance of energy transfer between the system and the surroundings can be expressed by the following equation:ĭelta U is the change in energy, q is energy transferred as heat to or from the system and w is energy transferred as work to or from the system. Sublimation of CO 2 requires energy and this is transferred as heat to the system (CO 2) from the surroundings showing that sublimation is an endothermic process. The system (gaseous CO 2) is expending energy in the form of work. ![]() The gaseous CO 2 expands within the plastic bag, lifting the bag and the book against the force of gravity and exerting a force against the surface and surrounding air. The bag, book, surface beneath the bag, and air outside the bag are the surroundings. In the case of this demonstration gaseous CO 2 is the system. ∆U is the change in energy q is the energy transferred as heat w is the energy transferred as work This is expressed by the following equation: ∆U = q + w For a system, heat and work are transferred between the system and the surroundings. This demo also illustrates the first law of thermodynamics. This energy is called the enthalpy of sublimation:Īn example of the sublimation of frozen water to gas is when frost evaporates in the morning. Sublimation is an endothermic process, absorbing energy like evaporation or melting. ![]() ![]() Sublimation is the process of the conversion of a solid directly to a gas. Place a book or other object on the bag to emphasize the work being done by the gas on the surroundings.Observe the dry ice sublimating and the CO 2 gas expanding within the bag.Using the tongs, place the dry ice in the bag.Must get CO 2 from the stockroom prior to class. Phone book (or other heavy item) for placing on top of bag.The dry ice sublimes producing CO 2 gas, which expands within the plastic bag, doing work on the surroundings. Subjects: Thermodynamics, work, energy, solid propertiesĭescription: Dry ice is placed in a plastic bag and sealed. 7.4 Sublimation of Dry Ice in a Sealed Plastic Bag ![]()
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December 2022
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