GCSE Rates: the fundamentals & exam tekkers

Added: 2026-05-26

[00:00:00]Welcome to Mr. Burch Chemistry. I'm going to help you improve by at least one grade with the fundamental information and some absolutely golden exam techers. Let's get into it. Okay, so we are going to take a look at um the idea of rate of reaction.

[00:00:21]Okay. Well, first of all, what do we mean by rate? When we're talking about rate, we're effectively meaning um the amount of change over a period of time.

[00:00:33]So it could be um the change in volume um uh uh over a certain period of time.

[00:00:41]It could be the amount of mass that decreases over a period of time. So again when we're talking about change um perhaps it's the volume or um perhaps it is the mass divided by time and that time might be in um seconds or um it um might be in minutes which is why the units of rate are always going to be what changed divided by uh time. So for example, it might be um centimeters cubed per minute, maybe the volume of carbon dioxide produced um over a certain period of time or it might be um the number of uh grams that the mass has gone down by per second.

[00:01:37]Okay? But what I need you to remember please is um uh this absolutely key equation here. Rate is change divided by time. Now it might be that you get a wordy type question that says what is rate? You write down change divided by time or just understand what rate is because that's going to help you um uh determining what the units are. Equally, it might help you when it comes to planning an investigation to uh to measure the the rate of a reaction.

[00:02:10]Okay. Um when we're talking about rate, um what we need to do is um think about how that rate changes over time. Uh and as you might imagine if this is a set of scales here um and this is time um we might imagine that we might have uh volume uh on our y axis and rate over time decreases.

[00:02:35]Let's have a little think about why that is. Well, if we start looking here we can see again note my language please that the gradient is steepest. Let's write that in. gradient steepest at the beginning or at the start. Nice little one mark answer there. Okay, let's not lose sight of that. So, we and the reason it's um uh fastest at the start um is because there are more particles. That's the time when you've got the most reactant particles that hopefully are going to collide with a minimum amount of energy um and turn into our products. But we can start seeing that over time the the uh rate starts to slow down. Look here we can see here that the gradient is less steep. So at the start it's very steep but as time goes on it becomes less steep. And we can see here this is how we know that the reaction has stopped because we've got this plateau. The gradient is zero at this point. gradient equals zero when the reaction has stopped. I.e. there are no more reactant particles to collide and create our products.

[00:03:56]Now remember, you're better than you think you are. Follow the process through. Score high. If that was useful, hit subscribe.