What Makes It React? Target 5-1

Target 5-1 We observed the Iodine Clock demo and saw a chemical reaction occur. We know it was a chemical reaction because we saw a sudden, unexpected color change. So…what makes the reaction happen??

Explore Consider the reaction H2 + O2  H2O You have H2 and O2 molecules in your groups (reactants) Perform the reaction using the atoms you were given. Think about what has to happen in order to make products.

BRAinstorm What happened during the reaction? Draw a particle diagram on your white board to show the reaction process

BRAINSTORM Recall that activation energy is the energy required to break bonds and start a reaction Where did the activation energy come from in your model activity? Where do you think the activation energy comes from in a real reaction with atoms?

Recap: Kinetic Particle Theory Kinetic Particle Theory is our best scientific explanation for how particles move and interact All matter is made of particles (atoms/molecules) All particles have kinetic energy (they vibrate and/or move around) Particles with more kinetic energy move faster The STATE and BEHAVIOR of matter is determined by the amount of kinetic energy the sample has.

So, Reactions… Reactions occur when 2 or more particles are behaving in ways that allow them to interact with each other Do you think particles ALWAYS interact with other particles?

Collision Theory Our best scientific explanation for when and how particles react is collision theory Collision Theory says that a chemical reaction will occur if 2 particles interact in an “effective collision” Particles must have enough kinetic energy to break bonds during the collision Particles must be reactive to each other Particles must be in the correct orientation to attract each other (bonds in the right places)

COLLISion Theory

Collision Theory In order for a chemical reaction to occur, there must be enough effective collisions for new products to form and accumulate. The more effective collisions occur, the more products will form.

Explore You have H2 and O2 molecules in your groups (reactants) Consider the reaction H2 + O2  H2O You have H2 and O2 molecules in your groups (reactants) Perform the reaction using the atoms you were given. You have 30 seconds to produce as much H2O as possible.

Brainstorm Compare your results to other groups Was every group able to make the same amount of H2O? Why not?

Collision Theory In order for a chemical reaction to occur, there must be enough effective collisions for new products to form and accumulate. The more effective collisions occur, the more products will form. The rate of reaction describes how fast products are formed (how fast the reaction happens) Faster reaction = faster rate Faster rate = more effective collisions

In-class assignment You have been given a student model of a chemical reaction between KCl and NaF. Identify what the student did correctly and incorrectly in her model. Revise her model to more accurately show the reaction process. Use the claim-evidence-reasoning format to explain why your revised model is more accurate.

In-Class Assignment Share your revised models and explanations with a partner. What was something you liked about your partner’s model? If I asked you to revise your model AGAIN, what would you change or add? Why?

TEAM Assignment We know the iodine clock flasks contained H2O2 The beakers contained KI, H2SO4, and Na2SO4 H2O2 and KI react to form I2, H2O, and K2O: H2O2 + 2 KI  I2 + H2O + K2O Draw a revised particle diagram comparing the reaction in flask A and flask E. Write a revised claim-evidence-reasoning explanation for the differences in reaction A and reaction E.

WRAP UP So, what made the iodine clock react? Are there any other questions we can answer? Are there any new questions we have?

Reaction Rate What affects the rate of a reaction? The amount of reactants available More reactants = faster rate The kinetic energy of the reactants More kinetic energy = faster rate Remember that kinetic energy = temperature! The activation energy of the bonds in the reactants Lower activation energy = faster rate