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A beaker of water is set up and a spoonful of food placed under it is set on fire with...

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sherryseah | Student, Grade 9 | (Level 1) Salutatorian

Posted June 18, 2012 at 4:38 PM via web

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A beaker of water is set up and a spoonful of food placed under it is set on fire with a match stick. Why does the the temp. of the water rise significantly.

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted June 18, 2012 at 5:56 PM (Answer #1)

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If a spoonful of food is placed below a beaker of water and is set on fire using a match stick the temperature of water would not rise significantly.

The cause for any rise in the temperature of water in the beaker is the heat produced as a result of the oxidation of the food in the spoon. The maximum heat would be generated if the form of food in the spoon is fat as fat has the highest concentration of energy at 9 calories per gram; a normal tablespoon would hold approximately 15 ml of fat. As fat is less dense than water, the mass of fat that a tablespoon can hold would liberate close to 200 calories of heat.

With a specific heat of water at 1 cal/g*C, if the beaker has 100 ml of water there is an increase in temperature of around 2 degree C.

This is surely not a significant rise in temperature.

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