# Rates

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## The effect of surface area on the rate of reaction

Calcium Carbonate + Hydrochloric Acid- Calcium chloride + water + carbon dioxide

*How to measure the rate of reaction:

- By how fast a product is made

- by how fast a reactant is used up

Activation Energy-the minimum amount of energy needed for the particles to react is called this and is different for each reaction.

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## Catalysts

* Catalysts lowers activation energy

-This reduces how much heat energy needed to start the reaction

-Less energy in= cheaper products-more money/profit for the industry

*Catalysts speed up a reaction because more collisions will be successful (lead to a reaction)

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## Measuring rates of reaction

*Magnesium + Hydrochloric acid- Magnesium chloride + hydrogen

-When a graph is steep, its fast, less steep = slow and flat line shows th reaction has finished

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## Concentration and rate

*When there is a high concentration, there are less water particles, more acid particles.

-However when there is a low concentration, more water particles are present and there are less acid particles.

Higher concentration = faster rate of reaction*There are more reactant particles in a more concentrated solution, so more collisions will be happening, hence the rate of reaction is faster

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## Pressure

*Reactions involving gases are affected by the pressure of the gases present.

Low pressure= particles closer together- more collisions faster reactions

High pressure- particles spread out, less collisions, slower reactions

-Pressure only affects gases

Q. The harber process, in which nitrogen reacts with hydrogen to form ammonia, is carried out at 200 atmoshpere pressure. How and why will this affect the rate of reaction?

- The particles will be 200 times closr together and so will collide more often. The reaction will be much faster

Pressure cookers- The molecules move faster and collide more frequently and with more energy. Cooking times will be reduced.

Increased pressure= increased boiling points

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## Endothermic Reaction

-These are reactions that take in energy from the surroundings.

-The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder.

-The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are:

• electrolysis
• the reaction between ethanoic acid and sodium carbonate
• the thermal decomposition of calcium carbonate in a blast furnace
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## Exothermic Reaction

-These are reactions that transfer energy to the surroundings.

-The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter.

-The temperature increase can be detected using a thermometer. Some examples of exothermic reactions are:

• burning
• neutralisation reactions between acids and alkalis
• the reaction between water and calcium oxide
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## Question

Q:Explain why increasing temperature increases the rate of reaction? [4]

*Particles gain energy

*moves faster

*more frequent collisions

*more particles have energy greater than or equal to the activational energy

*more successful collisions= increased rate

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