Determining the Energy Change of a System
9
Problem: Gasoline burns in an engine. Heat released causes the gases to expand. Determine _E in J, kJ, and kcal if expanding gases do 451 J of work on the pistons and the system loses 325 J to the surroundings as heat.
Plan: System = reactants + products of reaction. Heat is released by the system, so q is negative. Pistons are pushed outward, so work is done by the system and w is negative. _E is the sum of q and w.
Solution: Calculating _E in J_
Converting from J to kJ:
Converting kJ to kcal:
Skill 6- 1. Interconverting energy units
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