c101_f10_1108

c101_f10_1108 - Review Energy transfer based on...

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Review Energy transfer based on conservation of energy 1. Energy transfer between substances is equal. 2. Direction of energy transfer is opposite. Δ E 1 = q 1 = -q 2 = - Δ E 2 Energy transfer for physical processes Δ E = amount of substance x cost for that substance. 1. Change in temperature: q = mc Δ T (or q = nC Δ T) 2. Change in phase: q = m Δ H (or n Δ H) Energy vs. enthalpy Δ E = change in energy = energy transfer (all conditions). Δ H = change in enthalpy = energy transfer at constant pressure (usual lab conditions of atmospheric pressure).
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Chemistry 101 Fall 2010 2 Standard enthalpy change ( Δ H ° ) is based on a chemical equation (mole ratio) at standard conditions of 1 bar of pressure and 25 ° C. For example, H 2 O(l) H 2 O(g) Δ H ° = +44.0 kJ/mol H 2 O(g) H 2 O(l) Δ H ° = -44.0 kJ/mol ° = pressure of 1 bar and T of 25 ° C (very close to atmospheric pressure of 1 atm and room temperature, i.e., typical lab conditions) Δ H ° = standard enthalpy change for a process Energy transfer for chemical processes (Section 6.6) C 3 H 8 (g) + 5 O 2 (g) 3 CO 2 (g) + 4 H 2 O(g) Δ H ° = -2220 kJ/mol (per mole of ???) 2220 kJ is released for every 1 mol C 3 H 8 and 5 mol O 2 and 3 mol CO 2 and 4 mol H 2 O.
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Chemistry 101 Fall 2010 3 Practice applying the mole ratio concept : How many grams of CO 2 are produced when 45.4 g propane are burned? How many kJ of energy are produced? MM (C 3 H 8 ) = 44.064 g/mol) MM (CO 2 ) = 44.010 g/mol 45.4 g C 3 H 8 ? g CO 2 45.4 g C 3 H 8 ? kJ
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Chemistry 101 Fall 2010 4 Example : conservation of energy How much water can be heated from 20.0 ° C to 100.0 ° C by burning 45.4 g propane (C 3 H 8 )?
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c101_f10_1108 - Review Energy transfer based on...

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