Rates of reaction of agar with different HCL concentrations

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Rates of Reaction

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Collision Theory

Different reactions can happen at different rates. The rate of the reaction tells us how quickly a chemical reaction happens. Reactions that occur slowly have a low rate of reaction. Reactions that happen quickly have a high rate of reaction. For example, rusting is a slow reaction: it has a low rate of reaction. Burning and explosions are very fast reactions: they have a high rate of reaction. For a chemical reaction to occur, the reactant particles must collide. But collisions with too little energy do not produce a reaction. The particles must have enough energy to overcome the activation energy in order for the collision to be successful in producing a reaction. Activation energy is the energy needed to start a reaction. The rate of reaction depends on the rate of successful collisions between reactant particles. The more successful collisions there are, the faster the rate of reaction. There are two ways to find the rate of a reaction:

  • Measure the rate at which a reactant is used up
  • Measure the rate at which a product is formed

The method chosen depends on the reaction being studied. Sometimes it is easier to measure the change in the amount of a reactant that has been used up; other times it is easier to measure the change in the amount of a product that has been produced.

Reactions where a single species falls decomposes in some way are slightly simpler because you won't be involved in worrying about the orientation of collisions. Reactions that involve collisions between more than two species are going to be extremely uncommon.

It is clear to understand that if you have a situation involving two species they can only react together if they come into contact with each other. Firstly they have to collide then they may react.

Why "may react"? It isn't enough for the two species to collide - they have to collide the right way around, and they have to collide with enough energy for bonds to break in the reactants.

(The probability of all this happening if your reaction needed a collision involving more than 2 particles is remote. All three (or more) particles would have to arrive at exactly the same point in space at the same time, with everything lined up exactly right, and having enough energy to react. This is highly unlikely to happen.)

Introduction

I was given some agar, hydrochloric acid, and heating equipment and told to investigate rates of reaction. I found that there were three variables I could test for:

-Temperature: Raising the temperature makes the particles collide more often in a certain time. Also, it makes it more likely that collisions result in a reaction.

-Surface area: this can be tested for by how much surface area is exposed. As you increase the surface area you increase the rate of reaction because we have more surface for reactions to happen, therefore more collisions between reactants.

-Concentration:

 Acid particles only react with agar when they collide. As you increase the concentration of the acid there are more acid particles in the same volume, thus there is a greater chance of acid particles colliding and reacting with particles of sodium carbonate, consequently there is an increase in the rate of reaction.

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pH:

HCL is a acid that in aqueous solution which can split into H+(aq) and Cl-(ag). pH stands for potentiometric hydrogen ion concentration so the concentration of H+(aq) determines the pH of the aqueous solution. In this case HCL is an acid because it has free H+. The concentration of HCL is determined by the concentration of H+(aq). The higher the concentration of H+(aq) in solution the higher the morality of the hydrochloric acid. For example 2m HCL will have more H+(aq) than 0.2M HCL.  

I decided to test concentration and change the concentration of the solution that I put ...

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This is a good report investigating the relationship between concentration and rate of reaction. It is written in a clear manner, but the author often repeats themselves. The method is well set out and easy to follow. Logical conclusions are drawn. Overall, this piece of work is 3 stars out of 5.