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  1. What is dry ice? What happens when the pressure under which it is stored is decreased to 1 atmosphere?
  2. At what temperature does solid ice and liquid water co-exist together?
  3. Why evaporation is called surface phenomenon?

Solid CO2 is known as dry ice.It is a good cooling agent and gives the temperature upto -78°C. At pressures below 5.13 atm and temperatures below −56.4 °C (−69.5 °F) (the triple point of CO2)it changes from solid to gas directly (sublimation).

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Dry ice is the solid form of carbon di oxide. It is commonly used as cooling agent as it provides temperature lower than what normal ice gives. Also, it sublimes with rising temperature, i.e. when temperature is increased or pressure is decreased, it directly changes its phase to gas without changing into liquid phase.

So, at 1 atm pressure, it sublimes.

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2)at 0 degree celcius

( I was not sure but ....it's a meritnation certified answer so it's correct!)

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3)Surface phenomenon is the phenomenon where only surface of any substance or object is involved in the process. On the other hand, bulk phenomenon refers to the phenomenon where whole of the substance or object is involved in the process and is affected in bulk completely. In evaporation, only the molecules of the liquid present on the surface of the liquid leave the liquid state and change into vapour state. It does not affect the molecules present in the bulk of the liquid. Thus, evaporation is a surface phenomena. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.

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1) Dry ice is the solid form of carbon di oxide. It is commonly used as cooling agent as it provides temperature lower than what normal ice gives. Also, it sublimes with rising temperature, i.e. when temperature is increased or pressure is decreased, it directly changes its phase to gas without changing into liquid phase.So, at 1 atm pressure, it sublimes.2) The triple point of water lies at 0 0 C. At triple point the three phases of water (solid, liquid, gas) solid ice, liquid water, and water vapours co-exist together.3)Surface phenomenon is the phenomenon where only surface of any substance or object is involved in the process. On the other hand, bulk phenomenon refers to the phenomenon where whole of the substance or object is involved in the process and is affected in bulk completely. In evaporation, only the molecules of the liquid present on the surface of the liquid leave the liquid state and change into vapour state. It does not affect the molecules present in the bulk of the liquid. Thus, evaporation is a surface phenomena. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.
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