Vernier Software & Technology

# Rate Determination and Activation Energy

## Introduction

An important part of the kinetic analysis of a chemical reaction is to determine the activation energy, Ea. Activation energy can be defined as the energy necessary to initiate an otherwise spontaneous chemical reaction so that it will continue to react without the need for additional energy. An example of activation energy is the combustion of paper. The reaction of cellulose and oxygen is spontaneous, but you need to initiate the combustion by adding activation energy from a lit match.

In this experiment you will investigate the reaction of crystal violet with sodium hydroxide. Crystal violet, in aqueous solution, is often used as an indicator in biochemical testing. The reaction of this organic molecule with sodium hydroxide can be simplified by abbreviating the chemical formula for crystal violet as CV.

${\text{C}}{{\text{V}}^{\text{ + }}}{\text{ }}{\text{(aq) + O}}{{\text{H}}^{\text{ - }}}{\text{ (aq)}} \to {\text{CVOH (aq)}}$

As the reaction proceeds, the violet-colored CV+ reactant will slowly change to a colorless product, following the typical behavior of an indicator. You will measure the color change with a Vernier Colorimeter or a Vernier Spectrometer. You can assume that absorbance is directly proportional to the concentration of crystal violet according to Beer’s law.

The molar concentration of the sodium hydroxide, NaOH, solution will be much greater than the concentration of crystal violet. This ensures that the reaction, which is first order with respect to crystal violet, will be first order overall (with respect to all reactants) throughout the experiment. You will monitor the reaction at different temperatures, while keeping the initial concentrations of the reactants the same for each trial. In this way, you will observe and measure the effect of temperature change on the rate of the reaction. From this information you will be able to calculate the activation energy, Ea, or the reaction.

## Objectives

In this experiment, you will

• React solutions of crystal violet and sodium hydroxide at four different temperatures.
• Measure and record the effect of temperature on the reaction rate and rate constant.
• Calculate the activation energy, Ea, for the reaction.

## Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

### Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

## Advanced Chemistry with Vernier

See other experiments from the lab book.

 1 The Determination of a Chemical Formula 2 The Determination of the Percent Water in a Compound 3 The Molar Mass of a Volatile Liquid 4 Using Freezing-Point Depression to Find Molecular Weight 5 The Molar Volume of a Gas 6 Standardizing a Solution of Sodium Hydroxide 7 Acid-Base Titration 8 An Oxidation-Reduction Titration: The Reaction of Fe2+ and Ce4+ 9 Determining the Mole Ratios in a Chemical Reaction 10 The Determination of an Equilibrium Constant 11 Investigating Indicators 12 The Decomposition of Hydrogen Peroxide 13 Determining the Enthalpy of a Chemical Reaction 14A Separation and Qualitative Analysis of Cations 14B Separation and Qualitative Analysis of Anions 15A The Synthesis of Alum 15B The Analysis of Alum 16 Conductimetric Titration and Gravimetric Determination of a Precipitate 17 Determining the Concentration of a Solution: Beer's Law 18 Liquid Chromatography 19 Buffers 20 Electrochemistry: Voltaic Cells 21 Electroplating 22 The Synthesis and Analysis of Aspirin 23 Determining the Ksp of Calcium Hydroxide 24 Determining Ka by the Half-Titration of a Weak Acid 25 The Rate and Order of a Chemical Reaction 26 The Enthalpy of Neutralization of Phosphoric Acid 27 α, β, and γ 28 Radiation Shielding 29 The Base Hydrolysis of Ethyl Acetate 30 Exploring the Properties of Gases 31 Determining Avogadro's Number 32 Potentiometric Titration of Hydrogen Peroxide 33 Determining the Half-Life of an Isotope 34 Vapor Pressure and Heat of Vaporization 35 Rate Determination and Activation Energy

### Experiment 35 from Advanced Chemistry with Vernier Lab Book

#### Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.