Reaction Kinetics
When a reaction takes place, it occurs because the reactant molecules collide with enough energy to cause an effective collision. When this happens, the particles of reactants "react" to form product particles. There is a prevailing thought about how a reaction takes place, it is called Collision Theory. This theory states that when particles collide, they transfer energy. If enough energy is transferred during these collisions, the reactant molecules will overcome the "activation energy barrier." This is kind of like the first hill on a roller coaster. Once the molecules get to the top of the hill, they have gained enough energy through collisions to convert into products. There are 4 factors that affect how quickly or slowly (the rate) a reaction would take place. They are:
1. The particle size- smaller particles have more surface area in contact with each other and will react quicker. Charcoal dust will burn much quicker than a large chunk of charcoal.
2. The reactant concentration- If the reactants are solutions, the higher the concentration (amount of solute) will cause the reaction to go quicker. This is due to the fact that there are more particles colliding.
3. The temperature- The warmer a reaction is, the quicker it will react. This is due to the movement of the particles in a higher temperature. Higher temperatures equal higher kinetic energy of particles, so they will react quicker.
4. Use of a catalyst- A catalyst is a chemical that will speed up the rate of a reaction without reacting itself. It lowers the activation energy barrier, thus causing the reaction to move quicker.
1. The particle size- smaller particles have more surface area in contact with each other and will react quicker. Charcoal dust will burn much quicker than a large chunk of charcoal.
2. The reactant concentration- If the reactants are solutions, the higher the concentration (amount of solute) will cause the reaction to go quicker. This is due to the fact that there are more particles colliding.
3. The temperature- The warmer a reaction is, the quicker it will react. This is due to the movement of the particles in a higher temperature. Higher temperatures equal higher kinetic energy of particles, so they will react quicker.
4. Use of a catalyst- A catalyst is a chemical that will speed up the rate of a reaction without reacting itself. It lowers the activation energy barrier, thus causing the reaction to move quicker.
Equilibrium
Sometimes there are reactions that go to completion in one direction, reactants turn into products. Sometimes, there are reactions that are reversible, meaning, they start out going forward, but then once enough products are formed, those products will now start to "work backwards" and convert into some of the original reactants. This is called a state of equilibrium. This happens with reversible reactions.
When you are looking at a reversible reaction, you want to be able to write an equilibrium expression, otherwise known as a "K expression." The "K" stands for equilibrium constant. The steps to write a K expression is simple. The general form for a K expression is K = [products]/[reactants] and you would raise the concentration of each product or reactant to its coefficient in the balanced equation. See the picture to the left. Also, refer to this example: If you have the reaction aA + bB <-- --> cC + dD, (where A, B, C & D are chemicals in a reaction and a, b, c & d are the coefficients in the reaction), you would simply write
K = ([C]^c[D]^d)/([A]^a[B]^b).
If the value for K is greater than 1, then the forward reaction is favored, meaning there are more product concentration than reactant concentration at equilibrium.
If the value for K is less than 1, then the reverse reaction is favored, meaning there are more reactant concentration than product concentration at equilibrium.
When you are looking at a reversible reaction, you want to be able to write an equilibrium expression, otherwise known as a "K expression." The "K" stands for equilibrium constant. The steps to write a K expression is simple. The general form for a K expression is K = [products]/[reactants] and you would raise the concentration of each product or reactant to its coefficient in the balanced equation. See the picture to the left. Also, refer to this example: If you have the reaction aA + bB <-- --> cC + dD, (where A, B, C & D are chemicals in a reaction and a, b, c & d are the coefficients in the reaction), you would simply write
K = ([C]^c[D]^d)/([A]^a[B]^b).
If the value for K is greater than 1, then the forward reaction is favored, meaning there are more product concentration than reactant concentration at equilibrium.
If the value for K is less than 1, then the reverse reaction is favored, meaning there are more reactant concentration than product concentration at equilibrium.
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