Specific Heat Calorimetry Calculating Heat Transferred Q m

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Specific Heat Calorimetry

Specific Heat Calorimetry

Calculating Heat Transferred Q = m. C T Q = amount of heat transferred

Calculating Heat Transferred Q = m. C T Q = amount of heat transferred m = mass of substance C = specific heat capacity of the substance. T = temperature change = Tfinal – Tinitial

Calorimeter source

Calorimeter source

Another calorimeter source

Another calorimeter source

Heat in Chemical Reactions n n Changes in heat energy are measured by The

Heat in Chemical Reactions n n Changes in heat energy are measured by The “universe” is contained in a styrofoam cup. n The “enviroment” is the water. **** n The “system” is whatever we put in the water.

Calorimetry Energy lost = Energy gained Difficult to monitor the “system. ” Easy to

Calorimetry Energy lost = Energy gained Difficult to monitor the “system. ” Easy to monitor the “environment” – that’s the water! Energy lost/gained by environment = Energy gained/lost by system

Calorimetry n n 10 grams of Na. OH are dissolved in 100 g of

Calorimetry n n 10 grams of Na. OH are dissolved in 100 g of water. The temperature of the water increases from 22 C to 30 C. Was the dissolving process endothermic or exothermic & how do you know? Exothermic – the temperature of the environment increased.

Dissolving n What’s happening when the Na. OH dissolves? Add H 2 O Close

Dissolving n What’s happening when the Na. OH dissolves? Add H 2 O Close together. Not interacting with H 2 O. Pulled apart & interacting with H 2 O.

Calorimetry n Calculate the energy released by the Na. OH in the previous problem

Calorimetry n Calculate the energy released by the Na. OH in the previous problem as it dissolved in the water. Energy lost by Na. OH = Energy gained by water. Easier to calculate from H 2 O perspective. Q = m. C T Q = energy (joules) M = mass (grams) C = specific heat capacity (Table B) T = temperature change = Tf - Ti

Calorimetry & Q = m. C T n n n The temperature of the

Calorimetry & Q = m. C T n n n The temperature of the water increased from 22 C to 30 C -22 C = 8 C = T What mass? Well, the temperature change was for the water, so you want the mass of the water. m = 100 g. Same goes for specific heat capacity. We’re going to calculate the heat absorbed by the water. CH 20 = 4. 18 J/g

Q = m. C T n. Q = 100 g X 4. 18 J/g

Q = m. C T n. Q = 100 g X 4. 18 J/g X 8 C n. Q = 3344 Joules.

Expressing Heat Changes n n The heat content of a system at constant pressure

Expressing Heat Changes n n The heat content of a system at constant pressure is the same as a property called Heat released or absorbed (Q) by a reaction at constant pressure is the same as a change in enthalpy (r. H), therefore, Q = r. H.

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