Factors Affecting Reactions [Chemistry]

Topics: Chemical reaction, Chemical equilibrium, Catalysis Pages: 5 (593 words) Published: March 28, 2013
Factors Affecting Reactions
I. Factors Affecting Reactions [545]

• Every chemical proceeds at its own rate.

• By changing the conditions of the reaction, the rate of almost any reaction can be modified.

• The rate of a chemical reaction depends upon:

o Temperature

o Concentration

o Particle Size[SA]

o Catalyst

A. Temperature [545]

• Increasing the temperature causes molecules to move faster, so there’s an increased chance of them colliding with each other and reacting.

• Increasing the temperature also increases the average kinetic energy of the molecules

• Lowering the temperature slows down the reactions.

B. Concentration [545]

• Increasing the number of collisions speeds up the reaction rate. The more reactant molecules there are colliding, the faster the reaction will be

• Putting more particles into a fixed volume increases the concentration of reactants and the frequency of collision.

• Increased collision frequency leads to a higher reaction rate.

C. Particle Size [546]

• The total Surface Area [SA] of a solid or liquid reactant affects the reaction rate.

• Reaction depends on collisions. The more SA on which collisions can occur, the faster the reaction.

• The smaller the particle size, the larger is the SA for a given mass of particles.

• An increase in SA increases the amount of the reactant exposed for reaction which increases the reaction rate.

D. Catalysts [546-547]

• Catalysts are substances that increase the reaction rate without themselves being changed at the end of the reaction.

• They increase the reaction rate by lowering the activation energy for the reaction.

• An Inhibitor is a substance that interferes with the action of a catalyst [Decreases reaction].

• Thus the Inhibitor reduces the amount of functional catalyst available [Its poison to Catalyst]

• Reactions slow or stop when a catalyst is poisoned by an Inhibitor.

II. Reversible Reactions and Equilibrium

A. Reversible reactions [ 549-551]

• A reversible reaction is a reaction that reverts in either sides of a reaction when applying one of the following changes to:

o Temperature

o Pressure

o Concentration

• Certain products go from reactant to products

• Reversible reactions revert in any direction of the formula.

• Example:
2SO2 (g)+ O2 (g)( 2S03(g)

• Chemical Equilibrium: Upsetting the balance by applying one or more key factors will cause a change in balance, and the reactions will force its way into equilibrium

• Nothing is loss or gained during Chemical equilibrium.

B. Le Chatelier’s Principle [Lee -shat-le-eer]

• Le Chatelier’s Principle: How chemical equilibrium shifts when there is a change in

o Concentration

o Pressure

o Temperature

• These Principles are affected by chemical position:

C. Concentration

• Changing the amount or concentration at any reactant or product in a system at equilibrium disturbs the equilibrium.

• If the side of the reaction with fewer moles (If balanced) has been added more gas moles, the

Concentration (in other words the number of moles) will increase on the opposite side.

Add CO2

Direction Shift

H2CO3 [aq]CO2 [aq] + H2O [L]

Remove CO2

Direction Shift

D. Pressure

• A change on a system affects only gaseous equilibrium that have an unequal number of moles of reactants and products.

• This is due to gas moles getting compressed together.

• Less pressure will increase the side with the most gas moles and decrease the side with the least gas moles

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