1. Quantitative Energy Problems

2. Units For Measuring Quantities of Energy
Joules (J)
calories (cal)
Calories (Cal)
Kilocalories (kcal)
1 calorie = 4.18 J
1 kcal = 1 Cal = 1000 cal

3. Heat of Fusion (Hf) For melting and freezing
The amount of energy that needs to be transferred to melt 1 gram of a substance.
Is different for different substances.
Ex: Hf for water is 334 J/g

4. Heat of Vaporization (Hv)
For vaporization, evaporation, or condensation
The amount of energy that needs to be transferred to vaporize 1 g of a substance.
Different for different substances.
Ex: Hv for water is 2260 J/g

5. Heat Capacity (c)
The amount of energy needed to raise the temperature of 1 g of a substance by 1 ⁰C.
Different for different substances.
Ex: The heat capacity for liquid water is 4.18 J/ g ⁰C
4.18 J of energy will have to be transferred to raise the temperature of 1 g of water by 1 ⁰C.

6. Heat Capacity (c) Ex: The heat capacity of copper is 0.385 J/g ⁰C.
0.385 J of energy will have to be transferred to raise the temperature of 1 g of copper by 1 ⁰C.

7. Quantitative Problems for Phase Changes
In a phase change the quantity of energy transferred depends on a property of the substance and the size of the sample.
Q = m x Hf
Q = m x Hv

8. Examples:
1. How much energy does 130 g of water absorb if it all evaporates? 2. How much energy is transferred when 10.0 kg of ice melts?

9. Quantitative Problems for Temperature Changes
In a temperature change, the quantity of energy (Q) transferred depends on a property of the substance, the size of the sample, and how big the temperature change is.
Q = m x c x ∆ T

10. Examples:
A 200. g cup of water is heated from 23 ⁰C to ⁰C. How much energy does the water absorb?
In the Icy Hot lab, 43 kJ of energy were transferred to 630 g of water at 22 ⁰C. What will the final temperature of the water be?