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Published byJoshua Pollock Modified over 2 years ago

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25.3 Heat and Thermal Energy Imagine heating a cup of coffee to a temperature of 100°C. Next think about heating up 1,000 cups of coffee to 100°C. The final temperature is the same in both cases but the amount of energy needed is very different. Specific Heat Capacity Table

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Does it take the same amount of energy to heat 1 cup of water as compared to 1 gallon of water No…more energy to heat 1 gallon…..MORE MASS

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Do all materials change temperature at the same rate? No some heat faster than others. The SLOWER something heats, the HIGHER Heat Capacity. WATER has a very high HEAT CAPACITY. Takes a lot of energy to change the temperature. METALS have a LOW specific heat…. Doesnt take a lot of energy to change the temperature. WHERE IS IT BENEFICIAL FOR WATER TO HAVE A HIGH SPECIFIC HEAT?

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25.3 Specific Heat The temperature of gold rises quickly compared with water because its specific heat is much less than the specific heat of water.

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25.3 Specific Heat The specific heat is the quantity of heat it takes to raise the temperature of one kilogram of material by one degree Celsius.

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Which is going to take more energy….change the temperature 5oC or 100oC? Takes more energy to change it to 100oC. GREATER the temperature change, the more temperature needed.

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25.2 Calculate Heat One kilogram of water is heated in a microwave oven that delivers 500 watts of heat to the water. One watt is a flow of energy of one joule per second. If the water starts at 10°C, how much time does it take to heat up to 100°C?

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25.2 Heat Equation Q = mc(T 2 -T 1 ) Specific heat (J/kg o C) Mass (kg) Heat energy (J) Change in Temperature ( o C)

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How much energy is needed to raise 50 grams of water from 25oC to 75oC?

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Specific Heat / Heat Capacity

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STEPS OF EQUATIONS Determine whether Q is going IN or OUT Determine if ENDOTHERMIC or EXOTHERMIC…which graph? Determine location of energy change (ie. TEMP. CHANGE of S,L,G or melting/freezing or evaporating/condensing) **use appropriate C, Hf or Hv

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endothermic = increase in temp.

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exothermic (negative heat)

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How much heat is required to raise the temperature of water of 50 grams from 20oC to 80oC?

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How much heat is required to REDUCE the temperature of water of 50 grams from 80oC to 20oC?

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How much heat is required to raise the temperature of water of 50 grams from -20oC to -5.0oC?

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How much heat is required to raise the temperature of water of 50 grams from 120oC to 180oC?

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How much heat is required to MELT 50 grams of water?

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How much heat is required to CONDENSE 75% of 50 grams of water?

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#6 130 kcal x 4.18 kJ = kJ 1 kcal kJ x 1000 J = 543,400 joules 1 kJ convert 130 kcal = 543,400 joules 2.5 kg = 2500 grams

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