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Science Department
Grade 12
Chemistry
17.1 Reaction Process
The American Academy School aims to be a centre of academic excellence dedicated to
producing leaders and global citizens of the future
Name: _____________________Section: _________Date: __________________
• NGSS Standard:
Students who demonstrate understanding can:
HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects
of changing the temperature or concentration of the reacting particles on the rate at which a
reaction occurs. [Clarification Statement: Emphasis is on student reasoning that focuses on the
number and energy of collisions between molecules.] [Assessment Boundary: Assessment is limited
to simple reactions in which there are only two reactants; evidence from temperature, concentration,
and rate data; and qualitative relationships between rate and temperature.]
Chemical processes, their rates, and whether or not energy is stored or released can be
understood in terms of the collisions of molecules and the rearrangements of atoms into
new molecules, with consequent changes in the sum of all bond energies in the set of
molecules that are matched by changes in kinetic energy.
•
Lessons involved:
17.1 Reaction Process
17.2 Reaction rate
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• The unit activities & projects
The American Academy School aims to be a centre of academic excellence dedicated to
producing leaders and global citizens of the future
1. Design an experiment
2. Reactivity of metals with acids.
Link:
17.1 Reaction Process
Lesson objectives :
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2.
3.
4.
Explain the concept of reaction mechanism.
Use the collision theory to interpret chemical reactions.
Define activated complex.
Relate activation energy to enthalpy of reaction
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The American Academy School aims to be a centre of academic excellence dedicated to
producing leaders and global citizens of the future
Define:
• Reaction mechanism: is the step-by-step sequence of reactions by which
the overall chemical change occurs.
• Collision Theory: Reactant
molecules must collide with a
favorable orientation and with
sufficient energy to exceed the
activation energy required to
transform the reactants to
activated complex.
• A homogeneous reaction is a reaction whose reactants and products
exist in a single phase.
• Intermediates Species that appear in some steps but not in the net
equation.
• Activation energy (Ea) is the
minimum energy required to
transform the reactants into an
activated complex.
• Activated complex: A transitional
structure that results from an
effective collision and that persists
while old bonds are breaking and
new bonds are forming.
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The American Academy School aims to be a centre of academic excellence dedicated to
producing leaders and global citizens of the future
• Enthalpy of the Reactions: ∆E
Change in energy of the chemical reaction is either releasing energy (
exothermic) or absorbing energy ( Endothermic)
Endothermic
Exothermic
ER < Ep
( Energy of reactants is less than Energy
of products)
∆H = Ep - ER
= +ve
o
o
o
o
• Reaction Pathway Diagram:
Ea : Activation Energy of the
forward reaction.
Ea = EAC – E R
Ea ‘ : Activation energy of the
reverse reaction.
Ea ‘ = EAC – EP
∆H = Ep - ER
∆H = Ea - Ea ‘
ER > EP
( Energy of reactants is more
than Energy of products)
∆H = Ep - ER
= - ve