Which statement describes the phase change that occurs when dry ice is placed in an open container at room temperature? Dry ice undergoes sublimation, an exothermic change, at room temperature. Dry ice undergoes deposition, an endothermic change, at room temperature. Dry ice undergoes sublimation, an endothermic change, at room temperature.

Question

Which statement describes the phase change that occurs when dry ice is placed in an open container at room temperature? 	Dry ice undergoes sublimation, an exothermic change, at room temperature. 	Dry ice undergoes deposition, an endothermic change, at room temperature. 	Dry ice undergoes sublimation, an endothermic change, at room temperature.

ciarán95 · Answer

Carbon Dioxide is a substance which goes straight from a solid (dry ice) to a gas (sublimes) or from a gas to a solid (deposits) without a liquid state forming. At atmospheric pressure, the point at which these changes in state can occur (like the point where water changes state from a liquid to a gas at 100 degrees Celsius) is at -78.5 degrees Celsius. We usually associate room as being around 20 degrees Celsius. If we were to think of what would happen if we left ice out at room temperature for a while...we would find that it would gradually melt and turn to water. This would be exactly what the dry ice, or solid carbon dioxide, would be doing here, only no liquid state would be forming, instead a direct conversion to the carbon dioxide gas that is around us. It would be absorbing the heat from the higher temperature surroundings to increase its own temperature, quickly doing so to the point where it reached that critical -78.5 degrees Celsius temperature. An endothermic reaction occurs if the dry ice is absorbing heat/energy in changing from one form to another, while an exothermic reaction would occur if it was releasing energy in changing from one form to another. Hope that helps you! http://www.youtube.com/watch?v=HbXNQfHnI3w