Rate Experiments

Basics

• Rate of reaction measures how fast reactants are converted into products during a chemical reaction.
• It's crucial to understand that the speed of a reaction relies on several variables, such as reactant concentration, temperature, pressure, and the presence of catalysts.
• Rate experiments therefore aim to study these factors and their impacts on the pace of reactions.

Rate of Reaction Calculation

• The rate of reaction can be determined by observing changes in measurable quantities over time.
• This could be changes in the mass, volume or colour.
• For example, if a gas is produced as a product, the rate at which the gas is produced can be measured.
• If the reaction involves a solid getting used up, measuring the decrease in mass over time can give the rate of reaction.

Concentration and Pressure

• The concentration of reactants or the pressure of gaseous reactants directly affects the reaction rate.
• As concentration or pressure increases, so does the rate of reaction.
• This is because there are more reactive particles in a given volume, increasing the likelihood of successful collisions between particles.

Temperature

• The rate of reaction is heavily influenced by the temperature.
• When temperature increases, the rate of reaction speeds up.
• This is due to particles moving more rapidly and having a greater energy, hence they're more likely to successfully collide and react.

Catalysts

• A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway that has a lower activation energy.
• Importantly, the catalyst does not get used up in the reaction.
• Consequently, even a small amount of catalyst can significantly speed up the reaction.

Collision Theory

• The Collision Theory explains how reaction rate is influenced by the factors above.
• For a reaction to occur, reactant particles must collide with enough energy (activation energy) and in the correct orientation.
• Increasing temperature or reactant concentration/pressure and adding a catalyst all serve to increase the frequency of successful, productive collisions.

Experimental Techniques

• Various experimental techniques can be used in rate experiments.
• For gas production in a reaction, one could use a gas syringe to capture and measure produced gas, or place the reactants in a conical flask on a mass balance and observe the mass decrease.
• For colour change in a reaction, colourimetry can be used to track changes over time.
• These techniques give tangible, observable data on how reaction rate changes with different variables.