Rates of Reaction - HCl + Mg

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Planning:

I am going to investigate how acid concentration affects the rate of reaction. For this investigation, I am going to use magnesium and hydrochloric acid to test rates of reactions. When I put magnesium into the hydrochloric acid, they start reacting. Bubbles are seen in the solution and hydrogen gas is given off. I know it is hydrogen because when I light the gas with a splint, it makes a popping sound. This is an exothermic reaction because heat is given off as the reactants are used up.  

Word Equation:

Magnesium(s) + Hydrochloric Acid(l)  Magnesium Chloride(aq) + Hydrogen(g)

Symbol Equation:

Mg(s) + 2HCl(l)  MgCl2(aq) + H2(g)

Collision Theory:

Reactions can only happen when the reactant particles collide. This is called the collision theory. The collision theory states that only a fraction of collisions are successful because for the bond to break and form new bonds, the atoms must have sufficient energy and the right orientation at the moment of impact. This is called the activation energy.

There are four factors that affect the rate of reaction. These are temperature, concentration (pressure for air), size of solid particles (surface area) and catalyst.

Temperature:

The rate of reaction can be increased by increasing the temperature. From the collision theory, I know that reactants will only react if the atoms collide with sufficient energy. By increasing the temperature, the energy levels of the atoms involved in the reaction will be raised. The atoms move faster if the temperature is increased because they gain kinetic energy. Because they move faster, more collisions will occur in a space of time. Also, more successful collisions will occur because they will collide with enough energy to react.

Concentration:

Increasing the concentration will also increase the frequency of collisions the two reactants have. This makes collisions between the important particles more likely. The concentration of an acid is determined by its molar. Concentration is for liquids but it is pressure for air. If the air has a high pressure, the atoms will be closer together therefore, there will be more collisions.

Surface area:

Because one of the reactants is magnesium, the surface area of it will affect how fast the reaction goes. This is because the acid particles have to collide with the surface of the magnesium. So the larger the surface area, the faster the reaction will be. For the same mass of solid, smaller particles have a larger surface area than larger particles.

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Catalyst:

A catalyst gives the reactants a surface to stick to where they can collide with each other. This definitely increases the amount of collisions. Also, catalysts increase the rate of reaction by helping break chemical bonds in reactant metals and provide a ‘different pathway’ for the reaction.

Plan:

For this investigation, I will change the concentration of the hydrochloric acid. I will be measuring the rate of reaction by recording the amount of hydrogen gas given off using a gas syringe.

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