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Collision Theory of Reactions
A chemical reaction occurs when• collisions between molecules have sufficient energy
to break the bonds in the reactants.
• bonds between atoms of the reactants (N2 and O2) are broken and new bonds (NO) can form.
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Activation Energy
• The activation energy is the minimum energy needed for a reaction to take place.
• When a collision provides energy equal to or greater than the activation energy, product can form.
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C(s) + 2 H2(g) CH4(g) + 18 kcal
In an exothermic reaction,• heat is released.• the energy of the products is
less than the energy of the reactants.
• heat is a product.
Exothermic Reactions
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Endothermic Reactions
In an endothermic reaction • Heat is absorbed.• The energy of the products
is greater than the energy of the reactants.
• Heat is a reactant (added).
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
N2(g) + O2 (g) + 43.3 kcal 2NO(g)
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Summary
Reaction Energy Heat Type Change in Reaction
Endothermic Heat absorbed Reactant
Exothermic Heat released Product
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Learning Check
Identify each reaction as
1) exothermic or 2) endothermic.
A. N2 + 3 H2 2 NH3 + 22 kcal
B. CaCO3 + 133 kcal CaO + CO2
C. 2 SO2 + O2 2 SO3 + heat
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Solution
Identify each reaction as
1) exothermic or 2) endothermic.
1 A. N2 + 3 H2 2 NH3 + 22 kcal
2 B. CaCO3 + 133 kcal CaO + CO2
1 C. 2 SO2 + O2 2 SO3 + heat
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Rate of Reaction
Reaction rate
• is the speed at which reactant is used up.
• is the speed at which product forms.
• increases when temperature rises because reacting molecules move faster providing more colliding molecules with energy of activation.
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Reaction Rate and Catalysts
A catalyst
• increases the rate of a reaction.
• lowers the energy of activation.
• is not used up during the reaction.
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Learning Check
State the effect of each on the rate of reaction as:
1) increases 2) decreases 3) no change
A. increasing the temperature.
B. removing some of the reactants.
C. adding a catalyst.
D. placing the reaction flask in ice.
E. increasing the concentration of one of the reactants.
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Solution
State the effect of each on the rate of reaction as:
1) increases 2) decreases 3) no change
1 A. increasing the temperature.
2 B. removing some of the reactants.
1 C. adding a catalyst.
2 D. placing the reaction flask in ice.
1 E. increasing the concentration of one of the reactants.
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Learning Check
Indicate the effect of each factor listed on the rate of thefollowing reaction as 1) increases 2) decreases 3) none.
2 CO(g) + O2(g) 2 CO2 (g)
A. raising the temperature
B. adding O2
C. adding a catalyst
D. lowering the temperature
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Solution
Indicate the effect of each factor listed on the rate of thefollowing reaction as 1) increases 2) decreases 3) none:
2CO(g) + O2(g) 2CO2 (g)
1 A. raising the temperature
1 B. adding O2
1 C. adding a catalyst
2 D. lowering the temperature