Energy & Chemical Reactions. I.Kinetics – area of chemistry concerned with rates of chemical reactions A.Reaction Rates 1.The change of concentration.
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I. Kinetics – area of chemistry concerned with rates of chemical reactions
A. Reaction Rates1. The change of concentration of reactants in a
unit of time2. Rate or speed of a reaction depends upon 2 or
more molecules colliding so that reactant bonds break and new product bonds form
B. Reaction rates are affected by:1. Nature of Reactants2. Temperature
• As temp. ↑, reactant particles speed up = more collisions• Increasing the temp. 10oC doubles reaction
rate3. Surface area - More surface area allows more
contact between reactants = faster reaction rate4. Concentration - ↑ concentration of 1 or more
reactants ↑ # of collision = faster reaction rate5. Catalyts – speed up reaction rates without being
permanently changed
II. Heat of ReactionsA. Review of Terms
1. Exothermic – heat is released by reactants, or given off
2. Endothermic - heat is absorbed by reactants from surroundings
3. Enthalpy (H) – total energy content of a substance• Also called Heat of Reaction, the heat given off
or absorbed during a chemical reaction (ΔH)4. Entropy (S) – measure of randomness or disorder
in a system
B. Activation Energy1. Energy is needed to move reactants into a
temporary group of atoms = activated complex2. As an activated complex, reactant particles
rearrange to from products3. Activation Energy – amount of energy needed
to move reactants into the activated complex
C. Heat of Reaction (ΔH)1. Also known as Enthalpy, the heat given off or
absorbed by reactants during a reaction2. (ΔH) = P.E.(products) – P.E.(reactants)3. Negative (-ΔH) = exothermic reaction• Can be written as a product
4. Positive (ΔH) = endothermic reaction• Can be written as a reactant
D. Effect of a Catalyst1. Lowers amount of activation energy needed to
form an activation complex2. Only changes the potential energy of the
activation complex. Everything else remains the same!
E. Entropy & Spontaneous Reactions1. Reactions tend to move from a point of high
energy to low energy with an increase in Entropy2. Spontaneous Reactions = reactions that move
from high energy to low energy with an increase in entropy
3. Gibbs Free Energy (G) – indicates how spontaneous a reaction is• Is determined by the effects of heat, temp., and
entropy• ΔG = ΔH - T ΔS• - ΔG for a reaction = spontaneous• + ΔG for a reaction = not spontaneous
F. Reversible Reactions1. Every reaction is exothermic in one direction
and endothermic in the other.
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