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J
Unit 4. Kinetics+Equilibrium4.4 What is endothermic and exothermic
reactions? March 15, 2011
Do Now:
Going over questions from yesterday
AIM: How do we distinguish between endothermic and exothermic reactions?
ENDOTHERMIC REACTIONS
DEFINITION
reactions that take in energy (heat)
heat is absorbed from the surroundings
EXAMPLES
solid liquid (ice cream melting)
liquid gas (boiling water)
solid gas
melting
vaporization
sublimation
Where is the heat?
• 2H2O(g) + heat ↔ 2H2(g) + O2(g)
• 2H2O(g) + 103 kJ ↔ 2H2(g) + O2(g)
• 2POCl3(g) + energy ↔ 2PCl3(g) + O2(g)
Circle where the heat is located. Indicate whether it is a reactant or a product
KEY IDEA
endothermic reaction
sample absorbs heat
heat is on the left side (reactant side)
EXOTHERMIC REACTIONS
DEFINITION
Reactions that release energy (heat)
EXAMPLE
gas liquid (rain)
liquid solid (making ice cubes)
gas solid
condensation
freezing
deposition
Where is the heat?
• 8H2 + S8 8H2S + heat
• 8H2 + S8 8H2S + 1026 J
Circle where the heat is located. Indicate whether it is a reactant or a product
KEY IDEA
exothermic reaction sample releases heat
heat is on the right side (product side)
INDEPENDENT PRACTICE
1. To be collected at the end of CLASS!
2. COME SEE ME AFTER SCHOOL IF YOU NEED TO MAKE UP WORK!