Next Generation Science Standards

Performance Expectation

Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.

• Clarification Statement: Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules.
• Assessment Boundary: Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.

Atoms are basically really, really, really tiny versions of bumper cars. Most of the time they're just bouncing off the walls, but sometimes they bump into other atoms and a chemical reaction happens. Just like with real bumper cars, the faster you're going and the more cars there are out there, the more likely you are to crash.

In this performance expectation, students will explain how increasing the temperature or concentration of particles affects the movement of atoms and the rate at which a chemical reaction will happen. Hopefully no one gets whiplash.

Put on your helmet, we're talking collisions in these activity ideas:

• Assign students to be a sodium atom, a chlorine atom, or a water molecule. Start with equal numbers of each and have students mingle around until all of the sodium atoms have paired with all of the chlorine atoms. Then explain that you are going to raise the temperature so students will need to move as quickly as is safely possible (no broken bones). Discuss how temperature affects the movement of atoms and how quickly they were able to find their partner. Then tell students that you are going to raise the concentration of sodium atoms and have half of the water atoms switch to chlorine and sodium. Repeat the process and then discuss how this changed the speed at which they were able to find a partner.
• Have students take a tour of this chemical reaction rate simulator. It's fairly basic, but has some great visuals and allows students to adjust the temperature and observe the effects on the movement of particles and the rate of the reaction.
• Set up stations around the room with cards describing different chemical reactions. On the back of the card, include a description about a change in temperature or concentration that will occur during the reaction and have students predict how the equilibrium will change.
• Have students design an experiment to determine if the age-old advice to put your glow stick in the freezer to keep it glowing longer is actually going to work or is just playground "wisdom."

Disciplinary Core Ideas

PS1.B – Chemical Reactions: Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy.

Students got a sampler platter version of this idea in HS-PS1-4, so hopefully they don't look as petrified this time around. At this point, they should understand that atoms and molecules are constantly moving. Sometimes, in the midst of all that moving and grooving, they collide and a chemical reaction is born.

The focus here is on what we can do to speed up those chemical reactions. Students should know that when we raise the temperature, particles move faster. Yes, this is more of a physics concept, but we're all friends here.

The faster the particles move, the more they bump into each other. The more they bump into each other, the sooner they will find a particle they can react with, so we see an increase in the rate of reaction.

Students should also know that we can also increase the rate of a reaction by increasing the concentration of one of the components of our reaction. Increasing the concentration is sort of like choosing your prom date six months in advance. You've got lots of dateless candidates to choose from and you're going to end up finding a date much faster than the kid that waits until a week before when everyone is already taken.

Students should also understand that the movement of those atoms carries kinetic energy (physics strikes again!). As we increase the temperature, the particles move more quickly and the kinetic energy increases as well. When an atom reacts to make a molecule, that kinetic energy is converted into bond energy; so, as bond energy increases, kinetic energy decreases.

Hopefully your students are starting to get the hang of this idea. As they perform experiments and collect evidence, they should be able to really piece together the effects of temperature and concentration on the rate of a reaction. If you find them crouched at their lab bench in the fetal position, hook them up with some more confident chemists and encourage a little peer teaching.

Science and Engineering Practices

Constructing Explanations and Designing Solutions: Apply scientific principles and evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects.

Ask your students why their homework is late and we're sure they'll be able to come up with a semi-plausible explanation without blinking an eye. They may even be able to provide evidence in the form of a forged note.

Unfortunately, forgery doesn't get you very far in the scientific world. Students will learn that explaining how temperature and concentration affect the rate of a reaction will require actual evidence and a solid understanding of the scientific principles behind it.

Students will also experience the intoxicating mixture of fear and excitement that comes with unexpected results. In their explanation, they will need to not only explain what went right, but also account for any, er, technical difficulties that may occur while they're gathering their data. Overheating combustion reactions, for example, can turn into a quick mess or even an explosion. This is why we wear goggles, people!

Crosscutting Concepts

Patterns: Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.

Patterns are going to be your students' best friend when they're trying to explain what causes changes in reaction rates. We're not talking plaids versus stripes here. Instead, students will look for patterns in how factors like temperature and concentration affect reaction rates.

They'll be able to observe the obvious changes that occur during the course of the reaction, but will also need to relate those changes back to changes at the atomic level. They should see a pattern between the kinetic energy of the particles at the molecular level and the speed of the reaction at the macroscopic level.