When the collisions are taking place we need to make sure if they successful so that it is reaching the activation rate breaking the bonds allowing the rate of reaction to increase.
Surface Area-
(2cm) (1cm)
2x2=4 1x1=1
4x6=24cm2 1x6=6
6x8=48cm2
- More surface area= More surface for successful collision
- Increased rate of reaction
The more surface are there is for the particles to hit the higher the rate of Reaction should be. Between magnesium and hydrochloric acid the rate of reaction increases as you increase the surface area of the magnesium. The particles are more exposed within the acid when the surface area is greater. So as there is more exposure this increase leads to more successful collisions. With a smaller size of magnesium the speed is increased. Magnesium which has a smaller size in particle reacts more quickly than solids which have a larger size in particle. The acid starts to react from the edge of the magnesium this means that it takes longer for the reaction to finish. If you reduce the size of particles itself then it increases the rate of reaction as it also increases the surface area available for collisions to occur. This then has an effect on the number of collisions there are as it increases, however it does not affect the energy used.
Temperature-
- The higher the temperature the more energy the particles have.
- This means that they will be moving faster.
- This increases the rate of successful collisions.
- Particle shave more energy, so more likely to react when they collide
- This results in an increased or higher rate of reaction.
As you Increase the temperature it causes the rate of reaction to increase. So when you increase the temperature it then increases the kinetic energy within the particles, therefore there is a greater number of reactants who have enough energy for successful collision. As the reactant particles will also move more quickly the frequency of the collisions also increases. If the temperature is low the reactant particles consist of less energy. So when particles are heated they gain more energy. As they gain more energy this enables them to move around faster, this leads to an increase in colliding but also, as the energy is increased it then has a higher chance of a collision occurring with sufficient energy. Rate of reaction increases as the temperature increases.
The graph displays the minimum energy needed to start of the reaction of to break the bonds to allow the activation energy to work. It shows that near the end of the reaction new bonds are formed. It also shows that energy is released (exothermic reaction). As the temperature is higher the proportions of molecules have enough activation energy to react.
Catalyst-
- A chemical that is added to a reaction to speed up the rate, it is not used up!
- This increases overall rate of reaction.
- Catalysts lower the activation energy so particles are more likely to react
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Catalysts are a substance which is used to speed up chemical reaction without it being used up itself. It provides the reaction to take place at a faster rate. Catalysts increase the number of collisions between the particles of the substance which are going to react. The job of a catalyst is to decrease the activation energy; activation energy is the minimum amount of energy necessary for a reaction to take place. After adding the catalyst it allows them to react with less energy as the activation rate is decreased. As you add a catalyst it changes the rate of a reaction without itself being chemically changed when a new product is formed. The experiments which we will be doing are not going to be using catalysts as we are not going to be investigating the effects of the catalyst. If we were to use catalyst we would be using a positive catalyst as this speed up the reaction.
When adding a catalyst it could mean that during the process of the reaction the particles have enough kinetic energy to react making the reaction faster and more efficient. The catalyst does not increase any of the energy the reactant molecules have. When there is a reaction present with a catalyst it doesn’t take part as a reactant. The catalyst is not changed by the reaction, and will be the same throughout the reaction as it is not used up. ‘A catalyst is in a form of a transition metal’
What is Activation Energy?
Activation refers to the amount of energy required by certain chemicals for them to have a reaction. Some chemicals are able to react with each other immediately if placed next to each other. But there are other chemical types that need some extra push to gain some sort of activity between them. This extra push needed for chemical reaction is called activation energy.
Strategy
Methods of measuring rates of reaction:
Collecting and measuring a gas product, we use this strategy to measure the gas by capturing the gas released by the reaction in the conical flask, and then traveling through the delivery tube into the measuring cylinder. This enables us to measure the amount of product given off by the reaction in a curtain amount of time which is every 10 seconds. I have used this method because it is the most accurate out of the 4 methods.
In this experiment I will be measuring the effect of concentration on the rate of reaction between Magnesium and Hydrochloric acid. In this experiment I will be using different concentrations of acid to analyse the effect. We will be using one concentration through the experiment which will be the 2mol this is due to keep the test fair and accurate as we will be diluting it with water to make different level of concentrations for the same experiment.
In these experiments we will be testing five different concentrations contrasting the rate of reaction between Mg and HCL for all the concentrations. I will be using one concentration which will be the 2Mol.DP, and this will be used throughout my experiment. If I want to create a 1.5mol, DP acid I will be diluting the original concentration with water, this would be done by using a formula. There will be only variable changing through this experiment which is the concentrations; this will then determine what the independent variable is.
As we are not experimenting on how temperature affects the rate of reaction we will have to keep this the same. To keep the experiment fair and as accurate as we can we should not change the environment of the room we are experimenting in, i.e. leaving windows closed, or the lights on or off throughout the experiment.
When measuring out the magnesium strips you should ensure that they are consistent in length throughout the experiment. If it is changed it may cause the speed of the reaction to change as smaller pieces of magnesium tend to react faster and larger pieces tend to take more time to react. We will be measuring out the lengths by using a ruler as it will be giving us an idea of how long the magnesium strip will be. The structure of the magnesium strip we will be the same meaning that it will not be bent in any way shape or form and will be inserted in the conical flask the same way.
The volume of acid is always going to be 20cm cubed. We will try our best to keep this the same as it could affect the accuracy of the experiment and may change the concentration of the acids making the experiment not accurate. We will be using a measuring cylinder in order to keep the volume of the acid the same.
The sand paper will be used to scratch of any excess rust building up on the surface of the magnesium strip to make sure it is pure and not oxidised.
On our graph we will be using 3 reps to measure how long it takes for every concentration to react with the magnesium; this is also used to ensure accuracy and reliability. The 3 reps will rule out any anomalies. If there are small anomalies we are going to leave it however if they are large we will be changing them around so that our error bars remain small. We will be measuring the volume of hydrogen every 10 seconds up until 60, however if the reaction finishes before the time period we will terminate the experiment keeping the volume the same.
We will change the water for every experiment as the reaction gives of exothermic reaction heat and could transfer to the water making it warmer.
This strategy measures the loss of gas as the reaction happens. It is done by the scales measuring the loss of mass as the reaction happens and the to make sure it is accurate we use time intervals to see how long it takes for it to loose mass and the cotton wool is placed above so that nothing can insert the conical flask during the experiment only the gas is allowed to get out.
This strategy is used to see how long a solution takes to turn cloudy. It is used to see how long the reaction takes to dissolve making the cross on the piece of paper disappear.
We will be timing how long a solid takes to dissolve in a solution; it may use the same time intervals as the other 3 strategies. We will be timing it until however long it takes for the solid to completely disappear within the solution so there are no traces of solid left after the stop watch is stopped.
EQUIPMENT LIST
PRELIMINARY
For the preliminary test I will test different concentrations of acid. As we were unaware what the results of one concentration would be we done it using different concentrations contrasting the reaction rate, we used 2 mols/dm3, 1.7 mols/dm3 , 1.5 mols/dm3, 1.1 mols/dm3 and 0.5 mols/dm3. From these concentrations we resulted in that some reactions were very quick at the start and slowed down at the end and some were slow that we had to change the time intervals to 30 seconds this was only done for the 0.g mols/dm3 .
These results will help us determine the 5 concentrations that we need to use. 3mols/dm3 and 4mols/dm3 reacted too fast for us to take any readings therefore it was not suitable for our experiment. In our the preliminary we were only able to do 2 reps as there was not enough time to cover our experiments. In our preliminary it was hard to justify what concentrations we should use and it was hard to take any readings.
Safety
Safety/Risk Assessment:
For this investigation I will take specific cautions when investigating how different concentrations effect rate of reaction, this will be done before we start with our experimentation in order to fulfil our investigation. The cautions which will be considering are: keeping the level of magnesium and acid to a minimum preventing and hazards, make sure that teachers are informed if there is any hazard present such as spillages or broken glass, make sure no one runs around breaking the boundaries of the teachers rules, pushing are chairs in making sure no one trips over them as it could cause harm when they are doing their experiment as it involves acid and solid objects, goggles must be worn to prevent your eyes from being exposed to the acid, we should wear gloves to prevent any spillage of acid irritating your skin and we should ensure that we listen to instruction set by our teacher so our experiments run smoothly and we get the results we want. If we stick to these rules we are going to have a high chance of the investigation and experimentation running smoothly.
Method
- We got the equipment needed to proceed with the experiment. (BOWL, DELIVERY TUBE. CONICAL FLASK, BEEHIVE SHELF, STOP WATCH, HYRDOCHLOIC ACID, MAGNESIUM, GOGGLES AND MEASURING CYLINDER)
- We filled up the bowl allowing the beehive shelf to be submerged under the water so we are able to put the delivery tube through it.
- We used goggles to measure the hydrochloric acid/ diluted with water solution.
- We measured out 60cm of hydrochloric/diluted acid which allowed us to perform 3 experiments.
- We poured in 20cm of the solution into the conical flask
- We made a graph in our books which looked like this:
- We then measured out the magnesium strips and cut it into three pieces so all of them were the same size.
- As the equipment were already we inserted the magnesium strip into the conical flask and closed the delivery tube so that the gas is travelling through the tube, under the beehive shelf and into the measuring cylinder allowing us to take measurements every 10 seconds.
Results
This graph displays an exponential curve as, I have drawn this to show it. I have drawn this curve in order to make sure the points are all linked together. Tangent is needed in to find the gradient we plotted this by finding the steepest point on the graph another reason why we have drawn the tangent so that we are able to find the rate of reaction. In order to find the exact figures for the rate of reaction we done this by the change in y axis divided by the change in x axis. The results vary as some points have small difference this means the reliability is not that high. This graph has a positive trend on rate of reaction against concentration. This graph is displaying a first order reaction as the concentration is having a positive effect on the rate of reaction.
Evaluation
On the graph it is shows how the concentration of the acid has had a straight influence on the rate of reaction. As there is a higher amount of concentration this increases the rate of reaction, and is displayed as a second order graph. While carrying out the investigation we realised that there were minor mistakes affecting the results such as the error bars and the equipment which was used. Other issues present could’ve been the fact of the conical flask not being reliable enough as there is a second of hesitance when adding the magnesium as it depends how fast we closed the rubber top and therefore some hydrogen may be able to escape, this then has a direct effect on the error bars as it depends how big they are. However if we used different theory’s preventing these causes I believe that the errors would’ve been smaller as there are less errors causing problems with the results.
If we used a water bath to control the temperature of the conical flash I believe it would have been more reliable, because people were changing the temperature of the room as they opened the doors and windows. To keep the dilutions as accurate as possible we should have used scales measuring how much we used for every solution. I believe that even though we sanded down the magnesium it would have been more accurate if we weighed how much we were using for each experiment to keep the reliability high. We could’ve used the displacement of water theory which used the gas syringe preventing any gas from escaping.