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Gas Laws and Heat Measurement Formulas

Gas Laws and Heat Measurement Formulas. (Use with the Gas Laws/Heat and Its Measurement Worksheets. Boyle’s Law. A balloon has a volume of 8.0 L at a pressure of 90 kPa . What will be the new volume if the pressure drops to 40.0 kPa ? Boyle’s Formula = P 1 V 1 = P 2 V 2

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Gas Laws and Heat Measurement Formulas

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  1. Gas Laws and Heat Measurement Formulas (Use with the Gas Laws/Heat and Its Measurement Worksheets

  2. Boyle’s Law • A balloon has a volume of 8.0 L at a pressure of 90 kPa. What will be the new volume if the pressure drops to 40.0 kPa? Boyle’s Formula = P1V1 = P2V2 • P1 = 90.0 kPA V1 = 8.0 • P2 = 40.0 kPA V2 = ? So… P1V1 (90.0 kPa) (8.0 L) • V2 = P2 = 40.0 kPa= 18 L

  3. Charles’ Law Charles’ law states that the volume of a gas varies directly with Kelvin temperature. You add 273 to Celsius (oC + 273) and find the proportions: V1V2 T1 = T2 (Pressure must remain constant) A 3.0 L balloon at 10.0oC was placed in a container of ice water (2.0oC). What is the resulting volume? V1 = 3.0 L T1 = 283 K (10.0oC + 273) V2 = ? T2 = 275 K (2.0oC + 273)

  4. Charles’ Law 3.0 L = ? L 283 K 275K (3.0 x 275)825 283 = 283 = 2.92 L Notice that, when the temperature was lowered, the volume became lower.

  5. Heat and Its Measurement • Heat energy (Q) can be measured in units of calories (Cal) or joules (J). When there is a temperature change (Δ), you find the heat energy by mass x ΔT (TF – TI) x the specific heat capacity of the substance.

  6. Heat and Its Measurement Example: How many joules of heat are given off when 8.0 g of water heats up from 20oC to 80oC? The specific heat of water is 4.18 j/goC. Mass = 8.0 ΔT = 60 specific heat = 4.18 Q = Mass x ΔT x specific heat Q = 8.0 x 60 x 4.18 = 2006.4 J

  7. Heat and Its Measurement Example: How many joules of heat are given off when 8.0 g of water cools from 80oC to 20oC? The specific heat of water is 4.18 j/goC. Mass = 8.0 ΔT = - 60 specific heat = 4.18 Q = Mass x ΔT x specific heat Q = 8.0 x 60 x 4.18 = - 2006.4 J Because the water is cooling, it is an exothermic change (losing heat)

  8. Heat and Its Measurement If you are measuring heat during a phase change, then use the formula Q = mass x heat of fusion (freezing) or vaporization Ex: How many calories are given off when 60g of water at 0oC freezes? The heat of fusion is 79.72 cal/g. Q = 60g x 79.72 = 4783.2 Cal

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