Factors Influencing Rates - Video Tutorials & Practice Problems
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There are 4 major factors that directly influence how fast or slow a reaction proceeds.
Factors Influencing Rates
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Factors Influencing Rates Concept 1
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There are 4 major factors that directly influence how fast or slow a reaction proceeds. Now here we're going to say for reaction to occur, reactive molecules must collide with enough energy. And with this whole idea of energy in collisions, we have collision frequency and successful collisions. Now collision frequency is the number of molecule collisions per unit of time. And successful collisions are just those energetic collisions resulting in product formation. Because sometimes molecules may collide together, but they may not do it with the right amount of energy or force, and therefore products will not be made. So if we take a look here, we have molecules that are energized. They're energized and hit each other with enough force, and this results in successful collision where they're stuck together. If they don't have enough energy, then they're not gonna lead to a successful Collision. They will not stick together, and eventually they'll just bounce off one another. So keep this in mind. These are the fundamental things we need for any successful collision for chemical reaction to proceed. Click on the next video and let's go a little bit more in-depth in terms of these four factors that have a direct impact on these successful collisions.
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Factors Influencing Rates Concept 2
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The 4 factors that have a direct impact on influencing reaction rates include concentration of reactants, surface area of reactants, temperature, and catalysts. Now here, if we take a look at concentration of reactants first, we're going to say the condition is if we increase the reactant concentrations, what effect does this have on collisions? Well, increasing the amount of reactants within a mixture means there are gonna be more reactants floating around. This is gonna result in increase in collision frequency, because since there's more molecules floating around, you have a higher likelihood of them bouncing into each other. This results in an increase in your rate. Now surface area of reactants. Here, you wanna have a larger surface area. So we wanna increase our surface area. Usually when we talk about surface area for compounds, we can look at compounds as either being linear or branched. When we say linear, linear compounds have higher surface areas. Here we have a hydrocarbon. It's made up of CH3 CH2 CH2 CH3. Branched means that whereas in linear we just have a straight line of elements together, something that's branched has a portion of it that's sticking out. Here, this ch three part is a branching group. Branching decreases our surface area. So just remember, if we can increase the surface area of our reactants, that's gonna cause an increase in our collision frequency, which in itself again will cause an increase in our rate. Now temperature, we're gonna say here that increasing increasing our temperature is going to cause an increase in our collision frequencies. If you think of it in terms of your heating up your mixture, your your solution which has reactant molecules floating around, if you're heating it up, those molecules will absorb that extra external heat source and basically use it to power themselves up. This will cause them to move around with greater energy. If they're moving faster, they can bump into each other even faster. So this is gonna cause an increase in collision frequency because there's an increase in collision energy from absorbing the thermal energy. Now we're gonna say the rule of thumb is if we increase the temperature by just 10 degrees Celsius, this causes a doubling of our rate. So our rate would increase by 2 x. So increasing temperature, increases collisions, increases the force of the collisions because the molecules are moving faster. All of this causes an increase in our rate. Finally, a catalyst. We're gonna say the addition of a catalyst. Remember, addition of a catalyst causes a decrease in your activation energy. And that's a good thing because the lower your activation energy is, the more likely that your reactants can become products. So decreasing our activation energy will cause an increase in successful collisions, which in turn will cause an increase in your rate. So these are the 4 factors you need to keep in mind when dealing with reaction rates. Affecting them can have a big impact on how fast or slow your chemical reaction will proceed.
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Factors Influencing Rates Example 1
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Which of the following would cause the rate of a chemical reaction to slow? Alright. A, increase in temperature of the reactants. Remember the rule of thumb is if you're increasing the temperature of reactants, that's always gonna cause an increase in your rate because the molecules will absorb this thermal energy and use it to energize themselves, they'll move faster, hitting each other more often and with greater force. B, increase in concentration of the reactants. Well, if you're increasing the concentration of reactants, there's more reactants floating around, so they're more likely to hit each other, which increases their chances of successfully colliding together. So this would only increase your rate, not decrease it. C, increased surface area of the reactants. Increasing the surface of your area of your reactants always causes an increase in your rate because there's just more spots where things can connect together. So here, this always makes the rate faster. The answer here is increase in volume that the reactants take up. This is the answer. If we think about it, let's say we have a container that's this big, and in it we have some floating molecules. They have to collide in order to successfully, combine. But what would happen if I increase the the volume of the container while keeping the number of molecules the same? Right? Now I'm not I didn't actually count each dot from the first container, but just think of this visualization here. The container is bigger. Are the reactive molecules more likely or less likely to collide together now? They're less likely because there's so much more space between them. There's a lower chance of them finding each other, colliding, and then hopefully, some of those collisions lead to sticking together. Because remember, you can collide with each other, that doesn't guarantee you'll stick together. Right? So here, increasing the volume that the reactants, increase in volume that the reactants take up means the increase in the container volume. This does not help reaction rate, it lowers it because reactive molecules are less likely to find each other. Right? So here, only option d would potentially slow down a chemical reaction.
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Problem
Problem
Which of the following reacting molecules are able to produce products the fastest?
A
B
C
D
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Problem
Problem
A chemist tries to burn sulfur in air and notices that it burns very slowly. Chemist then burns sulfur in pure oxygen and observes a brilliant blue flame. Which factor is affecting the reaction rate?
A
increase in temperature
B
the presence of a catalyst
C
increase in reactant concentration
D
physical state of reactants
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