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How much electrical energy, in joules, is consumed by a 75-W bulb burning for 1.0 hr?

EXAMPLE 14.1. Power and Energy Conversion. Solution. From the definition of a watt, 1 W = 1 J/s, we know that 75 W = 75 J/s. The bulb burns for. 60 min. 60 s. x. 1 h x. = 3600 s. 1 h. 1 min. Exercise 14.1A. Exercise 14.1B. 75 J. 3600 s x. = 270,000 J. 1 s.

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How much electrical energy, in joules, is consumed by a 75-W bulb burning for 1.0 hr?

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  1. EXAMPLE 14.1 Power and Energy Conversion Solution From the definition of a watt, 1 W = 1 J/s, we know that 75 W = 75 J/s. The bulb burns for 60 min 60 s x 1 h x = 3600 s 1 h 1 min Exercise 14.1A Exercise 14.1B 75 J 3600 s x = 270,000 J 1 s (a) How much electrical energy, in kilojoules, does a 1200-W space heater consume when it runs for 8.0 h? (b) How much energy is that in kilowatt hours? How much electrical energy, in joules, dos a 650-W microwave oven consume in heating a cup of coffee for 1.5 min? How much electrical energy, in joules, is consumed by a 75-W bulb burning for 1.0 hr?

  2. EXAMPLE 14.2 Energies of Chemical Reactions Solution We start with 15.0 mol C3H8 and use the balanced equation to form a conversion factor, just as we did with chemical conversions in Chapter 6. 2201 kJ 15.0 mol C3H8 x = 33,000 kJ 1 mol C3H8 Exercise 14.2A Exercise 14.2B The reaction of nitrogen and oxygen to form nitrogen monoxide (nitric oxide) requires an input of energy. N2(g) + O2(g) + 18.07 kJ  2 NO(g) How much energy is absorbed when 5.05 mol of N2 reacts with oxygen to NO? Photosynthesis is an endothermic reaction in which carbon dioxide and water are converted to sugars in a reaction that requires 15,000 kJ of energy for each 1.00 kg of glucose produced. How much energy, in kilojoules, is required to make 1.00 mol of glucose? Burning 1.00 mol of propane releases 2201 kJ of energy. C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(g) + 2201 kJ How much energy is released when 15.0 mol of propane is burned?

  3. EXAMPLE 14.3 Energy Changes in Chemical Reactions Solution The formula mass of propane (C3H8) is (3 x C) + (8 x H) = (3 x 12.0 u) + (8 x 1.0 u) = 36.0 + 8.0 u = 44.0 u The molar mass is therefore 44.0 g. Next, we use the molar mass to convert grams of propane to moles of propane. Now, proceeding as in Example 14.2, Exercise 14.3A Exercise 14.3B 1 mol C3H8 225 g C3H8x = 5.11 mol C3H8 How much energy, in kilocalories, is released when 4.42 g of methane is burned? CH4 + 2 O2 CO2 + 2 H2O + 803 kJ How much energy, in kilojoules, is absorbed when 0.528 g of N2 is converted to NO (see Exercise 14.2A)? 44.0 g C3H8 2201 kJ 5.11 mol C3H8 x = 11,200 kJ 1 mol C3H8 How much energy is released when 225 g of propane (see Example 14.2) is burned?

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