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

• 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?

• 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.