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L24-Energy_Balance_Non-_Reactive_Sym

# L24-Energy_Balance_Non-_Reactive_Sym - Energy Balancein...

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Energy Balance- in Non-Reactive System

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LEARNING OBJECTIVES By the end of this topic, you should be able to: Performed energy balance for non reactive system using heat capacity formulas
Recall: How to calc. ΔH or ΔU and associated with certain processes: specifically P at constant T T ENERGY BALANCES ENERGY BALANCES .dT Cv U Δ T2 T1 = .dT Cp H Δ T2 T1 = H Δ For Ideal gas:exact Solid or liq: good approximation Nonideal gas: valid only if V is constant Ideal gas:exact Nonideal gas: valid only if P is constant ΔP V H Δ = .dT Cp ΔP V H Δ T2 T1 + = Solid or liquid

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Heat capacity formulas Cv and Cp are physical properties of materials Heat capacities are functions of temperature Heat capacities are expressed in polynomial form e.g. Cp = a + bT + cT 2 + dT 3 Relationship exists between Cp and Cv in two cases: Liquids and solids: Cp Cv Ideal gases: Cp = Cv + R where R = gas constant ENERGY BALANCES ENERGY BALANCES
Heat capacity formulas Example: Assuming ideal gas behaviour, calculate the heat must be transferred of the following: Nitrogen contained in a liter-flask at an initial pressure of 3 bar is cooled from 90 o C to 30 o C Solution Involve energy balance for ___________ system Since this is a ___________ system, need to determine heat capacity at ________________________ by the relationship of Cp = Cv + R Need to determine heat capacity at ______________________ first ENERGY BALANCES ENERGY BALANCES

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Heat capacity formulas Example: Nitrogen contained in a liter-flask at an initial pressure of 3 bar is cooled from 90 o C to 30 o C Solution (cont.) Using Cp = Cv + R, solve for __________________. From the energy balance equation, we need to calculate ____. Then solve for Q. ENERGY BALANCES ENERGY BALANCES
Estimation of Heat capacities Polynomial expressions for Cp are experimental based Approximation used if tabulated formulas are not available Kopp’s rule - estimation of heat capacity at or near 20 o C (Table B.10) E.g. heat capacity of solid calcium hydroxide (C p ) Ca(OH) 2 = (C pa ) Ca + 2(C pa ) O + 2(C pa ) H (C p ) Ca(OH) 2 = [26 + (2x17) + (2x9.6)] = 79 J/mol.

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L24-Energy_Balance_Non-_Reactive_Sym - Energy Balancein...

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