Heat Calculations with Specific Heat What is heat? What is energy? How are they both measured?
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Transcript of Heat Calculations with Specific Heat What is heat? What is energy? How are they both measured?
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Heat Calculations with Specific Heat
What is heat?What is energy?
How are they both measured?
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What is heat?• (q) – transfer of energy from one object to
another because of temperature difference between objects
• form of energy • flows from warmer to cooler object• measured in joules
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What is energy?• (E) – ability or capacity to do work• measured in joules• detected by effects
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What is temperature?
• (T) – NOT a form of energy
• thought of as intensity of heat
• measured in C, F, or K
• amount of heat per unit of substance
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What is a Joule?• (J) – amount of energy produced when a force of
1 Newton acts over a distance of 1 meter• small amount of energy • 1 Newton ~ amount of force 40 pennies exerts on
the palm of your hand• striking a match releases 1050 J
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What is thermodynamics?
• THERMODYNAMICS deals with energy changes (∆ E) that
accompany chemical and physical properties
• TELL US whether a reaction is possible depending on:
- whether reaction occurs by itself (spontaneously) OR
- if reaction needs outside source of energy to proceed
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Laws of Thermodynamics
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What is heat capacity?• energy required to raise temperature of
substance by 1 °C • Every pure substance has unique heat capacity• Expressed as Joules • 1 Calorie = 4.184 Joule
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What is specific heat?• (Cp) energy required to raise temperature of substance by 1
°C
• Specific Heat varies depending on:• Type of substance• State of matter of substance (s, l, g)• Temperature of the reaction
• S.H. of ICE = 2060 J/kg°C• S.H. of liquid water = 4180 J/kg°C
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How do you measure heat?1. Mathematically using HEAT EQUATION• q = m x Cp x ∆T • How much energy would be needed to heat .450
kg of Copper metal from a temperature of 25 °C to 75 °C?
• Specific Heat of Copper at 25 °C = 385 J/kg °C• q = m (Cp) ∆T PLUG
AND CHUG!
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What is a Calorimeter?
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• You are boiling water to make spaghetti. When the water boils, does it all instantly vaporize? Why not, after all – it’s reached the boiling point?
• Video Animation
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• EX. How much heat is necessary to totally melt 5 g of ice at 0 C to liquid water at 0 C?
• EX. How much heat is necessary to change 5 g of water at 100 C to steam at 100 C?
• HEAT CALCULATIONS • q = m Cp T for substance WITHOUT a phase change△• q = m H△ fus when a substances freezes/melts
• q = m H△ vap when a substance evaporates/condenses• If a substances undergoes a phase change and changes
temperature, you must add all the heats together.