Aim # 22: How can we change the rate of a
chemical reaction?
H.W. # 22
Study class notes
Complete handout sheet
I Nature of the reactants- since bonds are broken
and formed in a reaction, the type of bonds is an
important factor affecting reaction rates.
Negligible bond breaking
and rearrangement → RAPID REACTION
e.g. ionic substances in solution
NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)
The (aq) reactants are already dissociated.
Significant bond breaking
and formation
→ SLOW REACTION
e.g. molecular substances
2H2(g) + O2(g) → 2H2O(g)
II Concentration- as concentration ↑,
collision frequency ↑,
reaction rate ↑
Homogeneous Reaction- a reaction in
which all the reactants are in the same
phase.
e.g. N2(g) + 3H2(g) → 2NH3(g)
As volume ↓, collisions ↑, reaction rate ↑
Heterogeneous Reaction- a reaction in
which the reactants are in more than one
phase.
e.g. 3O2(g) + 4Fe(s) → 2Fe2O3(s)
III Surface Area- for heterogeneous reactions,
as surface area ↑, collisions ↑,
and reaction rate ↑.
IV Temperature- an increase in temperature
increases the rate of a chemical reaction.
As particle speed ↑, collision rate ↑,
number of effective collisions ↑.
Generally, if temp. ↑ by 100C
the reaction rate doubles.
V Catalyst- a substance that speeds up a chemical
reaction without itself being permanently altered.
A catalyst does not initiate a chemical reaction.
without a catalyst
Potential
Energy
with a catalyst
Reaction Coordinate
1. At room temperature, which reaction would be
expected to have the fastest reaction rate?
1) Pb2+(aq) + S2-(aq) → PbS(s)
2) 2H2(g) + O2(g) → 2H2O(l)
3) N2(g) + 2O2(g) → 2NO3(g)
4) 2KClO3(s) → 2KCl(s) + 3O2(g)
2. As the number of moles per liter of a reactant in
a chemical reaction increases, the number of
collisions between reacting particles
1) increases 2) decreases 3) remains the
same
3. Under which conditions will the rate of a
chemical reaction always decrease?
1) The concentration of the reactants
decreases, and the temp. decreases.
2) The concentration of the reactants
decreases, and the temp. increases.
3) The concentration of the reactants
increases, and the temp. decreases.
4) The concentration of the reactants
increases, and the temp. increases.
4. A 1-cubic-centimeter cube of sodium reacts more rapidly
in water at 250C than does a 1-cubic-centimeter cube of
calcium at 250C. This difference in rate of reaction is
most closely associated with the different
1) surface area of the metal.
2) nature of the metals.
3) density of the metals.
4) concentrations of the metals.
5. Given the reaction:
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
The reaction occurs more rapidly when a
10-gram sample of Mg is powdered, rather than
in one piece, because powdered Mg has
1) less surface area
2) more surface area
3) a lower potential energy
4) a higher potential energy
6. when a catalyst is added to a chemical reaction, there is
a change in the
1) heat of reaction 3) potential energy of reactants
2) rate of reaction 4) potential energy of the products