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8. Explain what is happening in terms of temperature and energy during the vaporization of a liquid and why this happens:
PR E O V N IE LY W
9. Why does the temperature increase between changes of physical state?
ELABORATE: Calculating the energy absorbed during heating
`` As we have seen when energy is added to a system (e.g. naphthalene or
water) the temperature increases steadily until the melting point or boiling point. The rate at which the temperature increases depends on: • The rate at which the energy is added to the system, • The mass of the substance being heated • The specific heat of the substance.
`` The specific heat is the amount of energy required to raise the temperature of 1 g of the substance by 1°C. All substances have different specific heat values. The specific heat of water is 4.186 joules per degree Celsius per gram (4.186 J ⁄ °C ⁄ g) (equal to one calorie and often rounded to 4.2 J ⁄ °C ⁄ g).
`` Knowing the specific heat of a substance (such as water) allows us to
determine the amount of heat energy produced by a burning substance (such as natural gas). In our water heating example, the heat released by the burning of the gas in a Bunsen burner can be quantified by measuring the temperature change and the volume of water (1 mL of water = 1 gram).
Energy released = 4.2 x change in temperature (DT °C) x mL water = 4.2 x (50°C – 40°C) x 50 = 4.2 x 10 x 50 = 2100 J For a 10°C change in the temperature of 50 mL of water.
10. For the heating of water (investigation 1.2) calculate the energy that was produced by the Bunsen burner during the rise in temperature of the water from 10°C to 90°C:
(a) The energy required to heat 100 mL of water by 40°C:
(b) The energy required to heat 200 mL of water by 20°C:
AS NOT SR F OO OR M US E
11. Using the specific heat equation for water in the blue box above, calculate the following:
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12. The number you calculated in question 10 above is an underestimate of the energy actually produced by the Bunsen burner. Think about the set up of the investigation with the beaker of ice on a tripod above the Bunsen. Suggest some reasons why the Bunsen produces a lot more energy than you calculated (i.e. where is the energy going?):
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