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Factors Affecting Homogeneous Reactions - Concept

Teacher/Instructor Jonathan Fong
Jonathan Fong

M.Ed.,San Francisco State Univ.

Jonathan has been teaching since 2000 and currently teaches chemistry at a top-ranked high school in San Francisco.

Here we'll take a look at tips for factors that affect reaction rates and take a look at homogenous and heterogeneous reactions. There are actually four factors that affect reaction rates.

Factor number one is the nature of reactants. The nature of reactants basically tells you or depends upon their bond strengths and their structural formula. What that means is, so the bond strength, obviously the stronger the bond the harder it would be to break apart a reactant. It might slow down the rate of the reaction. When I have a lower bond strength, then it's easier to break my reactant, because it would take less energy to break that bond.

The structural formula also could determine like the intermolecular forces. Like if we have Dipole-Dipole or Hydrogen bonding, and so the structural formula would really affect that too because Lennard dispersion forces would be the weaker type of intermolecular force and then that might affect certain things. And also the bonds within your particular molecule, could also be affected by the structural formula.

Stronger bonds you can also have different configurations or arrangements. And so the nature reactants affects your reaction. Then the rest of them, I would liken to if you make Jell-O. The rest of these other three things would actually be pretty easy to remember. If you think about Jell-O, first thing they tell you is to heat up your water. The temperature increases. Basically what happens is that, your reactants basically collide more often. So what happens is temperature increases, reactants collide more often, and there's more energy available to break bonds. That's the reason why for Jell-O, they tell you boil your water.

The next thing you do is, when you put the Jell-O in, its surface area is the next factor that comes into play. They don't give you Jell-O in a block of Gelatin, they give it to you in a powder form. When surface area increases the number of collisions by your reactants basically increases and there's more opportunities for higher energy for collisions. And then also you have more surface area. This happens especially in heterogeneous reactions, where you have different phases. So like, if you notice the surface area of your Jell-O, your Jell-O would be a solid and then putting it into water which is a liquid. Basically a solid into a liquid, that would be a heterogeneous reaction. So this would be in heterogeneous reaction, that surface area would be the play factor. The greater the surface area the faster your reaction will occur.

Then the last one would be concentration. Then concentration would basically, the higher the concentration, that means the more reactants or more reactant molecules are available for collisions. More of them are available to react. Just like say you have a certain particular thing and you flood the area, with more of these items then you have a greater likelihood of affecting whatever you're trying to affect. Concentration, the higher the concentration the greater the reaction rate.

Then you might also see Catalyst thrown in here. Basically a catalyst remember does not get used up, but it speeds up a reaction. Then you could have a homogeneous catalyst which is a catalyst in the same phase as your reactants, or you could have heterogeneous catalyst which is in a different phase from your reactants.

Remember natureof reactants like how strong their bonds are, whether structural formula. Then like our Jell-O, example temperature, you heat things up, the molecules collide and react faster. Surface area, greater surface area, more collisions are available and then concentration, you increase the concentration you increase the likelihood of your reactants colliding. Then also catalysts. Catalysts speeds up reaction without itself getting used up.

So hopefully these tips and tricks you remember the Jell-O method helps you remember about factors that affect heterogeneous and homogeneous reactions and their reaction rates. Have a good one.