energy - simple calorimetry - specific heat of water exercises

Solution

Look at the experiment above. If the test tube contains 60 mls of water and calculate the amount of energy, in joules per gram of jelly bean.

Step 1. Calculate the mass loss of the jelly bean. This is the amount that was burnt to release its energy.
initital mass - final mass = 3.69 - 3.29 = 1.80 grams

Step 2 Calculate the temperature rise

initial -final = 27.9 - 23.0 =4.9°C

Step 3 calculate the amount of energy released
energy released = 4.18 X mass of water X temperature rise.
Energy released = 4.18 X 60 X 4.9= 1228.92Joules or 1.25KJ

Step 4 calculate the amount of energy per gram released by the jelly bean
energy per gram = 1228.92 / 0.4 = 3072.3 Joules/gram

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Solution

Look at the animation above. A jelly bean is burnt and energy released to heat the water. How much water is present in the test tube if the amount of energy absorbed by the water is 0.789 Kilojoules.

Step 1Calculate the temperature rise

initial -final = 27.9 - 23.0 =4.9°C

Step 2 Transform the formula below to make it equal to mass

energy = 4.18 X mass X temp. change

=> energy / (4.18 X temp.) = mass

Step 4 calculate the mass of water

789 /(4.18 X 4.9) = 38.53 mls

The kilojoules per gram on the packet of the jelly beans above reads 2.58 kilojoules per gram instead of 1.97kilojoules per gram. Explain why?

The setup to conduct the experiment is not ideal. Heat energy escapes into the air and is not absorbed by the water. The amount of energy that we are able to calculate, per gram, is less than that contained by the jelly beans. Industry uses well insulated instruments called calorimeters to measure heat energy.

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Solution

2.45 grams of a special type of confectionary is burnt in a well insulated container. 100 mls of water, present in the container, increased in temperature from 22.4°C to 24.6°C. Calculate the amount of energy per gram of confectionary.

Step 1Calculate the temperature rise

initial -final = 22.4 - 22.6 =2.2°C

Step 2calculate the amount of energy released
energy released = 4.18 X mass of water X temperature rise.
Energy released = 4.18 X 100 X 2.2 = 919.6Joules

Step 3 calculate the amount of energy per gram released by the confectionary
energy per gram 919.6/ 2.45 = 375.35 Joules/gram

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Simple calorimeter Specific heat of water exercises
1)Look at the experiment above. If the test tube contains 60 mls of water and calculate the amount of energy, in joules per gram of jelly bean.

Solution 2)a) Look at the animation above. A jelly bean is burnt and energy released to heat the water. How much water is present in the test tube if the amount of energy absorbed by the water is 0.789 Kilojoules. b) The kilojoules per gram on the packet of the jelly beans above reads 2.58 kilojoules per gram instead of 1.97kilojoules per gram. Explain why? Solution 3) 2.45 grams of a special type of confectionary was totally burnt in a well insulated container. 100 mls of water, present in the container, increased in temperature from 22.4°C to 24.6°C. Calculate the amount of energy per gram of confectionary. Solution
	4) Irene was asked to calculate the amount of energy per gram of an ice-cream stick. She set up the experiment as shown on the left. 80mls of water were placed in a test tube at a temperature of 22.7°C. 0.92 grams of the stick was burnt under the test tube as shown and the temperature rose to 32.6°C. Calculate the amount of energy released per gram of wood. Scan the picture on the left for the solution. Would the result above be higher or lower than the real energy content per gram of wood? Explain.

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