INVESTIGATING THE RATE OF REACTION BETWEEN MARBLE CHIPS AND HYDROCHLORIC ACID

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INVESTIGATING THE RATE OF REACTION BETWEEN MARBLE CHIPS AND HYDROCHLORIC ACID

Introduction

This chemistry investigation was performed to investigate the rate of reaction between Marble Chips (Calcium Carbonate - CaCl ) and Hydrochloric Acid (HCL). In this investigation I want to find out whether the concentration of Hydrochloric Acid effects the amount of Carbon Dioxide being given off when the acid is added to Marble Chips.

The reaction rate would tell me how fast or slow a chemical reaction is and there are four things that could affect this greatly, they are: -

? Concentration: An increase in concentration means there are more particles. More particles means there will be more collisions. This should increase the reaction rate.

? Surface Area: when one of the reactants is solid, the reaction can only take place at the surface of the solid. Breaking the solid into smaller pieces will increase the surface area exposed to the other reactant. This should increase the reaction rate.

? Temperature: since temperature is a measure of the motion of particles, increasing the temperature will cause the particles to move faster. When particles move faster, more collisions occur and the collisions are more violent. This should increase the reaction rate.

? Catalysts: catalysts are substances that change the rate of a chemical reaction without being changed in the reaction. Catalysts are most often used to speed up a chemical reaction. They do so by changing the steps needed between reactants and the formation of the products. If the number of steps can be reduced, the reaction rate should increase.

The Reaction Rate is often called the Collision Theory which describes the way temperature, concentration and surface area of the solid reactant affects the rate of reaction, by affecting collisions from particles. Particles react when they collide with sufficient energy. At a higher temperature collisions are more frequent and they also have more energy, both because particles are moving faster. At a higher concentration collisions are again more frequent, as there are more reactant particles in the liquid. Increase surface are of the solid again increases the frequency of collision between reacting particles, as the liquid reactant has greater contact with the solid one. The rate of reaction can also be increased by adding a catalyst, but there is not one of this used in this experiment.

reaction rate

the speed, or velocity, at which a chemical reaction proceeds, expressed in terms of the amount of a product formed per unit time or the amount of a reactant used per unit time. Thus, for the reaction of two compounds X and Y that form a product Z, the equation is X + Y Z, and the reaction rate may be given by the rate of increase of the concentration of Z or by the rate of decrease of the concentration of X or Y. Mathematically, the reaction rate is given by dCZ/dt, -dCX/dt, or -dCY/dt, in which C represents the concentration (e.g., moles per litre) of the species denoted by the subscript, and the symbol d/dt is the mathematical expression for the rate of change of some quantity with respect to time (the derivative with respect to time).

Chemical reactions proceed at different speeds depending on the nature of the reacting substances and the type of chemical transformation. In general, reactions in which ions (electrically charged particles) combine or separate occur very rapidly, while those in which covalent bonds are formed or broken are much slower. For a given set of reactants, the speed of the reaction will vary with the temperature or pressure imposed on the reacting system and the amounts of reactants used. Ordinarily the reaction will gradually slow down as the reactants become depleted. In some cases the addition of a substance not itself a reactant, called a catalyst, accelerates a reaction that normally takes place at a very low rate.

The reaction-rate constant, or the specific rate constant, is the proportionality constant in the equation that describes the relationship between the rate of a chemical reaction and the concentrations of the reacting substances. If r represents reaction rate, k is the symbol customarily used for the reaction-rate constant, and f(C) is an expression for the concentrations of the reactants, then the equation for these values is r = kf(C). If the reaction rate, or velocity, is visualized as being determined by two factors, one representing the amount of molecules present and the other the type and the condition of those molecules, then the rate constant is a quantity that represents the latter. The prediction, measurement, and interpretation of reaction rates are subjects of the branch of chemistry known as chemical kinetics.

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Reaction rate taken from the Encyclopaedia Britannica

Collision theory and temperature effects on rates

Kinetic theory says that molecules are in constant motion. The kinetic energy and molecule velocity increase with temperature. KE = [1/2][mv2]

Reactions usually require collisions between reactant molecules or atoms. The formation of bonds requires atoms to come close to one another. New bonds can form only if the atoms are close enough together to share electrons. Some collisions are not successful. These are called ineffective collisions. The particles simply hit and then rebound. This animation illustrates what happens in an ineffective collision. ...

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