Three commercial glow sticks are began. One is at room temperature (23°C). One is immersed in a warm water bath (80°C). It glows more brightly compared to the light stick at room temperature. The 3rd light stick is immersed in an ice water bath (0.0°C) or in liquid nitrogen. It glows dimly. This series of comparisons of the amount of light being given off, which is proportional to the rate of reaction, illustrates how temperature influences prices of reaction.

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Student Observation Table

Temperature

Relative Amount of Light

Relative Reaction Rate

Hot water (80°C)

Room temperature (23°C)

Cold water (0.0°C)

Videos:

http://www.youtube.com/watch?v=fBtCTcRYEUk

http://www.youtube.com/watch?v=RH8TcwsHsvc

A collection of Power Point Slides is obtainable to acagency this demonstration.

Allow around 5 minutes for this demonstration.


Curriculum Notes

This demonstration is commonly performed as soon as collision theory and determinants that influences the rate of reactions (temperature) are being disputed.

Learning Outcomes/Objectives

1. An rise in temperature rises the reactions price. A decrease in temperature decreases the reaction rate.

2.An rise in temperature rises the the average kinetic power of the molecules, which involves boosts the average rate of the molecules.

3. Temperature affects the reaction rate by influencing collision power and also hence, the fraction of collisions via energy exceeding the activation energy.

4. A reaction mechanism consists of a collection of measures at the molecular level. Adding up the actions yields the in its entirety overallreaction.


Lead Time
One day of lead time is compelled for this project.
Discussion

This demonstration shows the result of temperature on reaction price.Raising the temperature of a reactivity mixture outcomes in both even more constant and even more energetic molecular collisions.Increasing the temperature rises the average kinetic energy of the molecules.At higher temperatures molecular collisions are more likely to have enough power to form products.This boosts the rate of reactivity. At reduced temperatures,tbelow are fewer collisions and many of the collisions that do happen between reactants carry out not have sufficient energy to form assets. Because at any kind of temperature in a gas, liquid, or solution, tright here is a circulation of molecular speeds, some molecules will certainly have adequate energy that as soon as they collide a reaction will certainly occur. At reasonably cold temperatures reactions take place but tright here are fewer efficient reactions compared to the device at greater power.

In a chemoluminescent reactivity such as this one, at elevated temperature, the enhanced reaction rate can be viewed as raised brightness of the light being offered off by the light stick. At cold temperatures, the light stick glows much less brightly bereason in a offered time period, fewer reactant molecules are colliding through enough power to develop the assets.

The chemical reaction in a light stick typically requires a number of different procedures. A typical commercial light stick has a thin walled-glassampule containing hydrogen peroxide solution floating in a solution of a phenyl oxalate ester via a fluorescent dye.Throughout the reaction, an intermediate is developed which transfers energy to the fluorescent dye molecule. When the dye molecule absorbs energy, the energy is supplied to raise electrons to an excited state. When the dye molecule retransforms to the ground state, the excited electrons return to the ground state and also power in the form of light is emitted. E = hv Pholots are emitted.

Here's the sequence of occasions that take place as soon as the 2 remedies are combined:

The hydrogen peroxide oxidizes the phenyl oxalate ester, causing a chemical referred to as phenol and also an unsteady peroxyacid ester.The unsteady peroxyacid ester decomposes, leading to additional phenol and a cyclic peroxy compound.The cyclic peroxy compound decomposes to carbon dioxide.This decomplace releases power to the dye.The electrons in the dye atoms jump to a greater level, then fall earlier down, releasing energy in the create of light.

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Expansions of the demonstration

Using a light meter in a darkened room, the activation energy deserve to be measured by plotting ln(light intensity) vs. 1/T, T = temperature. The activation energy is about 56.4kJ/mole.

Discuss the impact that temperature has actually on the price of chemical reactions. Discuss how the power of activation obstacle is get over. Ask students which light stick will use up the reactants first. Discuss the principle that the intensity of light is proportionalto the reaction price. The faster the rate of reactivity, the sooner all the reactants are consumed and also the reaction ceases.


Allow around 5 minutes for this demonstration.Dim the lights.Snap and also shake the 3 light sticks so that they begin to glow.Place one of the light sticks in the beaker containing ice water and also an additional in the beaker containing the warm water. The 3rd light stick serves as a regulate. Leave the light sticks in their corresponding beakers for around thirty seconds.Withattract the light sticks from their beakers making use of the attached strings. Compare their relative brightness. The light stick that was immersed in the warm water should be brighter than the control stick at room temperature and the stick that was immersed in the ice water have to be dimmer than the control stick.
The demonstrator will certainly be working roughly extremely warm water in problems of impaired visibility (dim light). Be careful, warm water have the right to cause significant burns.Vapor push can build up in the heated light stick and the warmth weakens the plastic. Heat the water to 80°C not to the boiling point. Light sticks have actually been well-known to burst under problems of warm temperatures over 80°C. The demonstrator have to wear goggles to protect eyes. Students should be at least 3 meters amethod from the demonstration location.

References

1BassamZ.Shakashiri, Lightsticks (2.2).Chemical Demonstrations, A Handbook for Teachers of Chemisattempt, volume.1 (Madison: The Universityof Wisconsin Press, 1983) pp. 146-152.

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2.Bassam Z Shakhashiri, Lloyd G. Williams, Glen E. Dirreen, and also Ann Francis, “Cool-Light Chemiluminescence,” J. Chem. Educ., Vol. 58, 1981, 70–72. The dependence of reaction rates on temperature is demonstrated through chemiluminescent light sticks.

3. http://pubs.acs.org/cen/whatstuff/stuff/7703scit4.html (C&EN “What’s ThatStuff?”)