Lec 20 Feb 25 Wed

# Lec 20 Feb 25 Wed - 3.4 Heat transferred(or heat of...

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3.4 Heat transferred (or heat of reaction) at constant P : Change in enthalpy q rxn (const P) = Δ H rxn An EXTENSIVE property: depends on the amount of substance energy is extensive so is mass, and volume, Δ H, and heat capacity An INTENSIVE property: does NOT depend on the amount of substance temperature is intensive so is density, melting point, specific heat capacity and molar heat capacity Work in chemical reactions (7.4) The most common type of work encountered in chemical processes is either : -- work done by a gas (expansion ; w < 0) -- work done to a gas (compression; w > 0) Work = application of a force (F) on a gas over a distance (h) w = F × Δ h Write work in terms of pressure of the gas : F = pressure (P) × area (A) w = P × A × Δ h , Volume = A × Δ h w = - P Δ V for mass and acceleration: 1 J = 1 N m = 1 kg m/s 2 × m = kg m 2 /s 2 w = m a Δ h movement of a mass: F = mass x acceleration w = work done ON mass Why the negative sign ? When Δ V is positive ( gas expansion), the system is

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