Question

Your instructor gives you a 100 g of dry ice (solid carbon dioxide) at -100 °C. Through the course of an experiment, you end up with 100 g of gaseous carbon dioxide at 0 °C. Answer the following questions based on this data. Assume that no heat is lost to the outside environment during the experiment. The specific heats for solid and gaseous carbon dioxide are 0.296 and 0.203 cal/g-°C respectively. Remember, carbon dioxide sublimes from solid to gas at -78.5 °C at one atmosphere. The heat of sublimation for carbon dioxide for this phase change is 141 cal/g. (a) How much heat is required to change 100 g of dry ice at -78.5°C to 100 g of gaseous carbon dioxide at -78.5°C (3 points)? (b) How much heat is required to change 100 g of dry ice at -100°C to 100 g of gaseous carbon dioxide at 0 °C (4 points)? (c) How much heat is required to change 100 g of gaseous carbon dioxide at 0°C to 100 g of dry ice at -100 °C? Carefully explain your answer (3 points)

Answer 1

Data Page c : -100°C Dry ice (a) Lince there is no temperature change, and given heat of sublimation is 141 callg & Heat required to sublimate 100 g of chy ice : 700x1415 14100 calorie (6) Specific heat of cay ice = 0.296 callgo Specific heat af gawcows 10 : 0.203 call goc Initial temperature sublimate et - 78.5°c. so temperature change upto sublimation - 78.5 +100 - 21.5°C final temperetho Temp. change after sublimation : 780 5°C Heat required upto 78.5 c = 0.296x21.58 100 636.4 calorie Head required for sublimation at -76.5°C = 14100 calore Heat required to bring temperature at o'c = 0.203 X 78.5 X 100 Isa3.55 caloric Hence total heat required = 636-4+ 14100 + 1593.55 16329.95 calorie Initial temperat ure = 0°c Temperattive change upto sublimation = 78.5°c. Heat required upto - 785°c = 0.203 x 78.5X 150=1593.55 Heat required for convesion to dy ice = 14100 calonie heat required upto 100° c = 0.296* 21.55100 - 636.4 calorie Here total heat required: 1593.55 +14100+636.4 = 16 329.95 caloric