PPT Slide

DE = q + w The Sign Conventions of q, w, and _E

6

Units of Energy

• The SI unit is the joule (J), a derived unit : 1 J = 1 kg ï m 2 /s 2 .  Both heat and work are expressed in joules.

• The calorie (cal) was defined originally as the amount of energy  needed to raise the temperature of one gram of water by 1ƒC.

• The energy changes in chemical reactions are often large; use the  kilojoule (kJ):

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