chapter 5 chemical reactions and quantities...chapter 5 chemical reactions and quantities 5.9 energy...
TRANSCRIPT
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Chapter 5 Chemical Reactions and Quantities
5.9 Energy in Chemical Reactions
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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 the following 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 the following 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
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Summary of Factors That Increase Reaction Rate