1. Thermochemistry Enthalpy: change in heat

2. Energy and Change of State You do not have to write this When energy is added to a solid substance, its temperature increases until its melting point is reached. Upon the addition of more energy, the substance begins to melt.  The temperature remains the same until all the substance has melted. ****

3. Energy required to melt 1 gram of a substance at its melting point Enthalpy of Fusion (  H fus ) Heating Curve: ( For Water) Time -20 -10 0 Heating Ice (solid) Melting point (°C)  H fus

4. After the substance melts and if heating continues, the temperature will continue to rise until it reaches its boiling point. ۞The temperature remains the same until all the substance has boiled.*** Energy and Change of State

5. Energy required to vaporize 1 gram of a substance at its boiling point Enthalpy of Vaporization (  Hvap) Time -20 -10 0 Heating Ice Melting Point 100 Heating Water (liquid) Boiling Point  H vap (°C)  H fus

6. ► Important Formulas to Know ◄ When a substance is being heated, use the following formula: (inclined line) q = (m)(c)(  T) meltingboiling When a substance is melting or boiling, use the following formula: (flat line) q = (m) (  H fus or  H vap )

7. q = (m)(c)(  T) q = (m)(c)(  T) (C) = Specific Heat: - of ice = 2.06 J/g x °C - of water = 4.18 J/g x °C - of steam = 2.02 J/g x °C

8. q = (m) (  H fus or  H vap ) q = (m) (  H fus or  H vap ) Enthalpy Values for Water:  H fus = 334 J/g  H vap = 2260 J/g

9. Sample Problem #1 How much heat is required to melt 5.67g of ice? Q = (m)(ΔH fus ) Q = (5.67g)(334 J/g) Q =

10. Sample Problems 2.) How much energy is required to boil 85g of water? 3.) How much energy is required to convert 40g of ice at -10°C to steam at 150°C ? 4.) What is the final temperature when 1250 J of energy is added to 15g of water at 25°C ?

11. Sample Problem #5 How much energy is required to raise the temperature of 25g of water from 15°C to 75°C ?

12. Practice Problems 6.) How much energy is required to boil 50 grams of water? 7.) What is the final temperature when 2500 J of heat is added to 35 grams of water at 15 degrees Celsius? 8.) How much energy is required to convert 75 grams of ice at -20 degrees Celsius to steam at 125 degrees Celsius? (Hint: This problem has 5 steps!!)