Duncan is a college student studying for a chemistry exam this evening. He also

Question

Duncan is a college student studying for a chemistry exam this evening. He also plans to swimming at the school gym and have a dinner of ramen noodles. While the water for the ramen is heating, it absorbs energy as it gets hot. Later, while swimming, Duncan uses the potential energy in the food he has consumed. The following conversion factors may be useful in this problem: 1 cal. 4.184 J 1 kJ 1000 J Part A Duncan takes a break from studying and goes to the gym to swim laps. If swimming burns 785x105 cal per hour, how many kilojoules does swimming burn in that same amount of time? In other words, convert 7.85x105 cal to kilojoules. Express your answer numerically in kilojoules. 785 10 cal. Submit Hints My Answers Give up Review Part Part B This question will be shown after you complete previous question(s). Continue

Explanation / Answer

Ans. Part A: 7.85 x 105calorie                                                    ; [1 calorie = 4.184 J]

            = 7.85 x 105 x (4.184 J) = 32.8444 x 105J                         ; [1 J = 10-3 kJ]

            = 32.8444 x 105 x (10-3 kJ)

            = 32.8444 x 102 kJ = 3.28444 x 103 kJ   

Part B: Specific heat is defined as the amount of heat required by unit mass of a substance to increase its temperature by 1 degree Celsius (or 0F, K, etc.).

Among the give set of substances, a substance with highest value of specific heat requires maximum amount of heat required to increase their temperature by 250C- given all are at the same initial temperature with same initial mass.

            Specific heat of water                 = 4.184 J/g0C

Specific heat of Aluminum          = 0.900 J/g0C

            Specific heat of copper              = 0.386 J/g0C

            Specific heat of gold                  = 0.126 J/g0C

            Specific heat of stainless steel     = 0.502 J/g0C

Decreasing order = water > Aluminum > stainless steel > copper > gold

Part B2: A metal cup with lowest specific heat shows maximum increase in its temperature.

For example, from the above list (part B) of metals, suppose there are four metal cups, all of same mass and volume and at same initial temperature.

If a certain amount of hot water is poured into them, the gold cup with least specific heat increase its temperature rapidly and hottest one.

Order (hottest first) : Gold, copper, stainless steel, aluminum.

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