everyday calorimetry. whenever we heat water, its like using a calorimeter calorimeters are used to...
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Everyday Calorimetry
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whenever we heat water, its like using a calorimeter
calorimeters are used to compare quantities of different fuels that burn to boil water
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Different Heat Capacities Effects the Calculations
in an Everyday Calorimeter, we have to take into account that different materials heat up at different rates
nHm = -(mcΔtpot + mcΔtwater)
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Simple Calorimeter
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Example:
Calculate the enthalpy of combustion of 13g of butane C4H10 on a campfire stove that is used to heat a copper pot (500g) filled with 1.5L of water from 17C to 98C?
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when we use calorimeters to determine enthalpies, they may not be 100% efficient
an analysis of an experiment must take into account the varying amounts of heat energy that are lost to the immediate surroundings and not actually absorbed by water
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one way to determine the efficiency of a simple calorimeter is to calculate the energy released from fuel mass and its standard molar enthalpy of combustion
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alternatively the experimental molar enthalpy can be compared with the reference values
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remember:
Efficiency = output x 100%
input
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Example 1 The following data were obtained from an
experiment to measure the efficiency of a simple combustion calorimeter heated by a stearic acid candle
(ΔH (C18H36O2)= -1.13x104 kJ/mol)
What is the efficiency of the calorimeter?
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Aluminum Pot = 300g
Containing 150mL Water
Temperature Change = +25C
50g Stearic Acid Candle Burns
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Example 2 A particular basement hot water heater is
70.0% efficient. What mass of natural gas (assume methane) must burn in order to heat 250kg of water from 5.0°C to 40.0°C?