# How to do reaction rate problems Rate problems

Aug 20,  · Solution. Step 1: Find b rate B /rate A = b/coefficient of A b = coefficient of A x rate B /rate A b = 2 x / b = 2 x 3 b = 6 For every 2 moles of A, 6 Step 2: Find c rate B /rate A = c/coefficient of A c = coefficient of A x rate C /rate A c = 2 x / c = 2 x c = 3 For. Oct 18,  · Check out more MCAT lectures and prep materials on our website: educationcupcake.us Instructor: Dave CarlsonSolving Rate Problems Part 3 - Elementary R.

Rutger's University M. Kendal founded an academic how to start a promotional modeling agency company in Washington D. In her spare time she loves to explore new places. To unlock all 5, videos, start your free trial.

In class, you may often be asked to solve different types of reaction rate problems. When solving reaction rate problems, it is important to remember the reaction rate laws and the basics of balancing equations. Alright so when you're union of kinetics and you have rate law problems here's some practice problems that you might come across that are a little bit more difficult so if you have just wanted to talk of general rate laws you might want to look at the actual videos that we what is 21 guns about from before this.

So here's one practice problem that I want to talk about that talks about the concepts within it. Okay let's consider a solution where we have 0. So the rate law looks like this, it's second order rate, second order reaction and they're both in the first order. Okay at each question we're going to ask does the rate increase, decrease or remain the same and does k our rate constant increase, decrease or remain the same?

Okay so let's say we were to add water to the solution, how is that going to affect the rate? Well it's not going to affect k at all, k is never going to change except in one scenario and that's when temperature changes, so the rate law constant is actually going to be the same it's not going to be affected but what will be affected is the rate.

And why would the rate be affected, because we're diluting these guys, we're lowering the concentration and we add water we're lowering the concentration of the thioacetamide and the hydrogen ion. So the rate is actually going to be slower, which makes sense because according to our collision theory the concentration plays a major part in how fast the reaction goes.

Number 2, the reaction is heated to 75 degrees Celsius, well we're adding heat to this reaction so it should proceed faster but if you notice and so the reaction, the rate does increase in this case if we increase temperature but how is that shown here? Well k is temperature dependent so even though concentrations remain the same k will change when temperature increases. So yeah k will increase as well, it's the only time k will change. What if how to do reaction rate problems add sodium hydroxide to this solution?

Well why would that make a difference? Because nothing in here as sodium hydroxide it may dilute the system but the concentration it's actually going to be quite similar. So how to build a 100 million dollar company main thing that's actually going to affect is actually sodium hydroxide is going to have a reaction.

The reaction it'll, this is the base it will react with this acid and so will go down which will decrease the rate of reaction.

So this concentration is going to go down, this will remain the same, the rate is going to lower as well. So the k will not change at all because again k is only going to change when temperature changes. Okay, so that's one type of a problem that you might see, another type of a problem that you might see or dealing with this type of finding the actual rate law using data.

And we've talked that in the rate law, when we're dealing with rate laws and I talked to you about rate laws. But let's how to do reaction rate problems about how this problem might be a slight bit different, so you're supposed to figure out the rate when comparing 2 different trials. So let's look at trial b because these 2 are the same and we're going to look at how a is affected. So we're going to say okay the concentration of a and the second one is 8, the concentration of a and the first one is 2 and how is that going to affect my superscript?

Because don't forget the backload of the rate law is going to be rate equals k or rate constant times the concentration of a to some certain power to the concentration of b to some certain power. And don't forget these coefficients that you have in this reaction are not going to necessarily be the coefficients or the powers in your rate law. Let's actually, so right now it's time to find the powers so as A changes what's going to happen to rate, rate goes from it goes 4.

Okay so what 4 to the what power is going to equal 16, well we know 4 squared is equal 16 so m is going to equal 2. So alright, so I'm going to change this to 2, fantastic so now I need to do b. Well b is changed, there's no time when a is constant, so this is actually what makes it more difficult, there's no time when a is constant but b there is a time when b is changing.

So what do we do now if a, if we can't compare? Well we already know the superscript, we already know the order of a so we can use that to figure out the order of b. So let's go over here and say okay I know that, let's just compare 2 and 3. And so we're going to say okay Okay so this 16 over 8 is 2, 2 squared is 4 times 3 over 1. So we're going to divide both sides by 4, 2 to the n equals 8 over 4 which is 2 so n is going to equal 1.

So now I can change this to 1. So that is how you figure out, find how to recharge sms pack in airtel online rate law if something, if one of your, in your trials one of your reactants is not changing. That might something you might get in a more advance class like in honors class or something and this is how you go about doing it. So now we have our rate law and I would typically have to find our k value I'm not going to sit there and find our k value or the plugging charge problem how to do reaction rate problems if you're to find, we're then going to find the units for k and the units for k are pretty easy because if you remember k is equal to the units for k I'm going to write units, is equal to 1 over the molarity times the order of the reaction minus 1 times the unit of time in this case it's seconds, so it's times seconds.

Okay, so the next question might say, if we have, which one is the correct mechanism? So the mechanism just because this follows the rate law actually the mechanism is the slowest step in the reaction and actually has to be the one that follows the rate law. Meaning that there has to be a 2 in front of the a and a 1 in front of the b in the slow step of the mechanism in the rate step. And if you want to learn more about mechanism, actually there's a video on mechanism describing everything about them that you would want to know.

So here, which one is the correct mechanism? So here is the slow step, the slow step is a rate determining step. We would say from here, we would say our rate is equal to k times ay because our slow step tells us that however we can't have y in our rate law. So I can substitute y for b and say the rate in, if this was the mechanism, this would be the rate. However, we said the rate was this using our data, this cannot be right, so it must be this one.

But let's prove it, rate in this cases is this slow step so we're going to say okay rate equals k times a times y. Again y is in our rate law I can't in our rate law because it's not in our reaction. So I'm going to take y, y what chocolate works best in a chocolate fountain formed here and I'm going to change it to a times b so then I can say okay I'm going to rewrite this and say k equals a squared, b equals rate does this match our rate law?

Rate equals k, a squared b yes this is how to do reaction rate problems so this must be the correct mechanism. So these are the more difficult problems that you're going to come across when dealing with kinetics and rate laws, so just use the information that you know and actually try it Mathematically you can actually always figure something out, so rate law can be pretty difficult and as we didn't go there's actually even more integrated rate laws and things like that half life activation energy that you might deal with in Chemistry so but this just your basic honors rate how to do reaction rate problems problem.

Previous Unit Chemical Solutions. Next Unit Chemical Equilibrium. Kendal Orenstein. Thank you for watching the video. Start Your Free Trial Learn more. Kendal Orenstein Rutger's University M. Explanation Transcript In class, you may often be asked to solve different types of reaction rate problems. Chemistry Chemical Reaction Rates. Science Biology Chemistry Physics. English Grammar Writing Literature. All Rights Reserved.

Solution: Rate of chemical reaction in gas phase increases with; adding catalysts, increasing pressure or decreasing volume, increasing temperature. Thus, decreasing pressure and increasing volume decreases rate of reaction rate. I and III increases reaction rate. Use rates to solve word problems. For example, Charlie can type words in 9 minutes. How many words can Charlie type in 13 minutes? How to Determine Orders of Reaction In many kinetics problems, the first order of business (a pun) is to determine the order of a reaction. The order of a reaction is simply the sum of the exponents on the concentration terms for a rate law: Rate = k[A]x[B]y reaction order = x File Size: 12KB.

Rate of chemical reaction in gas phase increases with; adding catalysts, increasing pressure or decreasing volume, increasing temperature. Thus, decreasing pressure and increasing volume decreases rate of reaction rate. I and III increases reaction rate. Kinetic energies of X gas at temperatures 1 and 2 are given below. If temperature is changed from T 1 to T 2 , which ones of the followings increase? When you examine the graph, you can see that number of particles at T 2 is larger than number of particles at T 1.

We brush the area that shows number of particles in both temperatures in given graph below;. A joins the reaction and leave without any change in its structure, so it is catalyst but C is not catalyst.

III is false. If fast step of this reaction is;. If we reverse the fast step and sum it with following reaction we can find slow step of this reaction. Which ones of the followings increases rate of reaction in gas phase; I. Adding catalysts II. Decreasing pressure III. Increasing temperature IV. Increasing volume Solution: Rate of chemical reaction in gas phase increases with; adding catalysts, increasing pressure or decreasing volume, increasing temperature.

Rate of reaction II. Number of particles that are activated III. Average kinetic energy Solution: When you examine the graph, you can see that number of particles at T 2 is larger than number of particles at T 1. It is exothermic III.

A and C are catalysts Solution: We multiply second reaction with 2 and sum with reaction I. Solution: If we reverse the fast step and sum it with following reaction we can find slow step of this reaction. A reaction have slow and fast steps as given below; I. Reaction rate is found using slow step of reaction. Increasing activation energy decreases reaction rate. III is true. Tags: activation energy chemical kinetics factors affecting reaction rate rates of reactions reaction rate reaction rate exams and solutions.