heat
DESCRIPTION
TRANSCRIPT
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Heat
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Homework
• Read 15.2– Assessment 16-22
• Read p. 530 (Thermochemical Equations for changes of state)– Assessment Question 27
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Kinetic Theory of Matter (KTM)Kinetic Molecular Theory
• All matter is made of tiny particles that are in constant motion
• The rate of motion determines – the temperature of the substance– the state of matter of the substance
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Heat• Heat is defined as the total amount of kinetic
energy (so it depends on the amount of matter present)
• When energy is transferred from one object to another, it is known as Heat
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Temperature
• Temperature is defined as the average amount of kinetic energy
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Energy and Phase Changes
endothermic – a chemical reaction that requires energy be put in
- energy is a reactant
(more E needed to break existing bonds in the reactants than is released when the new bonds form in the products)
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sunlight + 6CO2(g) + H2O(l) C6H12O6(aq) + 6O2(g)
•Photosynthesis is endothermic
•Cooking is endothermic
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• exothermic- a chemical reaction that releases energy
- energy is a product
(more E is released than is required to break bonds in the initial reaction)
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•Reacting Zn and HCl is exothermic
Zn(s) + HCl (aq) ZnCl2(s) + H2(g)
•Reacting Na and Cl is exothermic
http://www.chemeddl.org/collections/whats_this/wt20080215/index.html
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Heat Calculations• Heat (q)
Energy transferred from an object at a higher temperature to an object at a lower temperature. (heat lost = -heat gained)
q = mcT q=mHfus
q=mHvap
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Heat Calculations• A 10.0g sample of iron at 50.4oC is cooled to
25.0oC in 50.0g of water. Calculate the amount of heat lost by the iron.
ciron= 0.449 J/goC
• A 2.1g ice cube at –8.0oC melts completely and warms to 12.5oC. How much heat was required?
Hfus ice = 334 J/g
cice = 2.03 J/goC
cwater = 4.18J/goC
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Some Helpful Constants
specific heats:gold = 0.129 J/g°Caluminum = 0.897 J/g°Cwater = 4.184 J/g°Ciron = 0.449 J/g°Csilver = 0.135 J/g°Cice = 2.03 J/g°CHfus water = 334 J/gHvap water = 2260 J/g
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Practice1. How much heat is required to raise the temperature of 68.0g of
aluminum from room temperature 24.0°C to 80.0°C?
2. A beaker containing 150.0g of water at 80.0°C is cooled to 50.0°C. How much heat is lost by the water?
3. A 75.0g chunk of ice at –15.0°C is warmed to 0.0°C, completely melted, then warmed to 25.0°C. How much energy did this process require?
4. If a 1.55g piece of stainless steel at 30.0°C absorbs 141.0 J of heat, what will its final temperature be?
5. An unknown sample of metal has a mass of 0.625g. It is heated from 25.0°C to 55.0°C with 2.42 J of energy. What is the specific heat of this metal? Identify the metal.