Reaction Rate Basics

Reaction Rates are affected by a few things. Without telling them the point, the students had a quick demo where they had to dissolve sugar cubes the fastest. 

The things that speed up reactions are:

• Temperature - warmer is faster
• Surface Area - small pieces have more surface area
• Concentration - the more water, the faster sugar will dissolve
• Catalyst - lowers the activation energy and speeds up the reaction
• Agitation - shaking or stirring increases the frequency of collisions.

Reaction Types

We started by talking about the simple definition of the terms, what the probably products and reactants are and went over a basic formula for the reaction types the students need to be familiar with.

Reaction Types include:

• synthesis
• decomposition
• singe replacement
• double replacement
• combustion
• endothermic
• exothermic
• oxidation-reduction
• neutralization

After discussing the basics, we drew cartoons of stick men and women going on dates to show how atoms move around in the simpler reactions. The picture posted is someone else's version of single replacement (see the one guy switches with the other). For more help with this, check here.

 Homework is to finish the Benchmark Review Sheet and J and I on the orange homework sheet

Balancing Equations

Students are learning to balance equations. Today they learned that reactants are what you start with and are on the left side of the equation. Products are on the right side of the arrow and are what is made by process of a chemical change.

Because of the Law of Conservation of Mass, the number of atoms have to be equal on both sides. To balance an equation, the coefficients are changed. Coefficients are the big numbers in front that tell you how many molecules there are. The subscripts (the little lower numbers) are not allowed to be changed because those are there to make neutrally bonded molecules (what we learned in the last unit.

By changing the coefficients and counting the number of atoms on both sides of the arrow, balancing can be achieved.

Polar vs NonPolar

Anyone who has ever had to share something with someone else knows that sometimes isn't exactly even. Covalent molecules or bonds are no different. 

If a molecules is nonpolar covalent, it is sharing its electrons equally. The best example of this is in diatomic molecules. Diatomic molecules are two of the same atom bonded together - so they would have exactly the same pull. Symmetrical molecules are also nonpolar.

 

Polar covalent bonds occur when electrons are not equally shared. One atom, usually more electronegative, has a stronger pull on the electrons and shares them unequally. The other atom that is less electronegative has a smaller hold on the electrons and is thus can be slightly positive. 

One way to remember this is... "Polar Bears do not share... equally."