Chemistry - Rates of Reaction

These cards give a brief overview of the chemistry unit 2 section rates of reaction.

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Rates of Reaction

- Knowing and controlling the rate of chemical reactions is important in living cells, in the laboratory and in industry.

- We can measure the rate of a chemical reaction by following the rate at which the reactants are used up.

- Alternitively, we can measure the rate at which products are made.

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Collision theory

- The minimum amount of energy that particles must have in order to react is called the activation energy.

- The rate of a reaction increases if the surface area of any solid reactant increases.

- Four main factors affect the rate of chemical reactions:

Temperature, Concentration or Pressure, Surface area, and the presence of a catalyst.

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The effect of temperature

- Reactions happen more quickly.

- A 10 degree increase in temperature at room temperature roughly doubles the rate of a reaction.

- The rate of a chemical reaction increases with temperature because the particles collide more often and they have more energy.

Factors affecting the rates of Reaction - particle collision theory model (c) Doc Brown (http://www.docbrown.info/page03/3_31rates/Image43.gif)Factors affecting the rates of Reaction - particle collision theory model (c) Doc Brown (http://www.docbrown.info/page03/3_31rates/Image44.gif)

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The effect of concentration

- Increasing the concentration of reactants increases the frequency of collisions between particles, increasing the rate of reaction.

- Increasing the pressure of reacting gases results in particles colliding more often, increasing the rate of reaction.

(http://t1.gstatic.com/images?q=tbn:ANd9GcQK9jJ1Jfc1f0PLPSa88ipQ1rfRRB5LkxLr9ZluY2GbEOGQP65y:adaptiveblue.img.s3.amazonaws.com/topics/p/collision_theory/small)

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The effect of catalysts

- A catalyst speeds up the rate of a chemical reaction.

- They are often very expensive, because they are made from precious metals. However, it is often cheaper to use a catalyst than to pay for the energy needed for higher temperatures or pressures in a reaction.

- A cataylst is NOT used up during a  chemical reaction. It merely provides a surface for the reacting particles to come together.

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