NAME
PERIOD
ENTHALPY AND HEATING CURVES
Learning Target:
Students will demonstrate understanding of heating curves by explaining what occurs on each point of a heating
curve. Students will also be able to calculate the total energy required for water to go through phase changes.
Academic Vocabulary: enthalpy. endothermic, exothermic, heating curve, enthalpy of fusion, enthalpy of
vaporization
I.
Enthalpy and Reactions
i.
Enthalpy (H ) is
a. Specifically,
b. Each reaction will have an
ii.
If H is negative,
a. Reactions that release heat are called
H2(g) + Cl2(g)  2HCl(g)
iii.
H = -185,000 J
If H is positive,
a. Reactions that require an input of energy (heat)
CO2(g) + 2H2O(g)  2O2(g) + CH4(g)
iv.
H = 890,000 J
To determine if a reaction is exothermic or endothermic,
a. If ΔH is positive
b. If ΔH is negative
v.
Check for Understanding
List the following as endothermic or exothermic:
N2(g) + O2(g) → 2NO(g)
C(s) + 2S(s) → CS2(l)
PCl3(g) + Cl2(g) ⇌ PCl5(g)
II.
Phases of Matter
i. There are 3 common phases of matter:
1.
2.
3.
H = 180.5 kJ
H = 92 kJ
H = -92.5 kJ
III.
Phase Change
I. A phase change is
II. To change phases
III. Melting and Evaporating Phase Changes
a. Solids
b. Liquids
c. These phase changes require
d. Breaking bonds
e. Adding energy is
f. H is
IV.
Condensation and Solidification Phase Changes
a. Gases
b. Liquids
c. These phase changes
d. Forming bonds
e. Releasing energy is
f. H is
V. Check for Understanding
List the following as endothermic or exothermic and justify your reasoning:
 Ice cubes melting

Freezing water

Steam from shower condensing into water droplets on mirror
 Boiling liquid
VI. Summary
IV.
Heating Curves
i. A heating curve is a graph of
ii. It describes
iii. What does heat do?
a. If a substance is heated, the heat can do ONE of these:
b.
c. BUT NEVER
d. A substance may never
e. When a solid substance is heated,
f.
Temperature will then
g. When a substance is completely melted,
h. Temperature stays
i. Once completely vaporized
V.
Enthalpy of Fusion
ΔHfusion :
-Hfusion:
VI.
Enthalpy of Vaporization
ΔHvaporization:
-ΔH vaporization:
Summary:
Example Problem: How much heat is required to melt 233 grams of ice into water, from -15°C to room temperature
(25°C)?
 The specific heat of ice is 2.03 J/g°C
 The specific heat of water is 4.18 J/g°C
 The ΔHfusion of water is 334 J/g