CH 6 notes

# 100 grams ch 4 x 1 mole ch 4 1605 grams ch 4 x 8903

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10.0 grams CH 4 x 1 mole CH 4 /16.05 grams CH 4 x -890.3 kJ/1 mole CH 4 = -560. kJ of heat produced 6.6 Measuring heats of reaction (q) Calorimeters are used in the lab to measure the heat released in a chemical reaction (see page 240 in chapter 6 for a picture) - q= CΔT o ΔT = Tfinal – Tinitial o C = heat capacity ( a constant with units of joules / °C ) is the quantity of heat need to raise the temperature of a substance one degree C (or 1 degree K). - q can also be calculated using the mass of a substance and the specific heat (S.H.) o q = (S.H.) x mass x ΔT o specific heat is the same as heat capacity except the constant is for a 1.0 gram sample. The mass is in grams. o The S.H. values are on page 6.1 pg 239 and you do not need to memorize these values. The higher the S.H., the more energy a substance can hold and are better insulators. Examine the values for solids, liquids and gases. Water has a VERY high specific heat, like most liquids. Solids and gases have low specific heats. 6.7 Hess’s Law = a chemical equation can be written as the sum of 2 or more steps and the ΔH for the overall reaction equals the sum of the ΔH’s for the individual steps. ΔH formation = the energy needed or released when a compound or molecule is formed - Pure elements and molecular gases have a ΔH formation = 0 (they are formed by the universe naturally).

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• Fall '11
• Coffman

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