Download Heat Calculations with Specific Heat

Heat Calculations
with Specific Heat
What is heat?
What is energy?
How are they both measured?
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
What is energy?
• (E) – ability or capacity to do work
• measured in joules
• detected by effects
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
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
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
Laws of Thermodynamics
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
What is specific heat?
• (Cp) energy required to raise temperature of
substance by 1 °C
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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
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!
What is a Calorimeter?
• 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
Heating Curve in Motion
• 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?
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HEAT CALCULATIONS 
q = m Cp △T for substance WITHOUT a phase change
q = m △Hfus when a substances freezes/melts
q = m △Hvap when a substance evaporates/condenses
If a substances undergoes a phase change and changes
temperature, you must add all the heats together.