Rates of reaction Flashcards
one general way to measure the rate of a reaction
Measure how fast one of the reactants is used up
Another general way to measure the rate of a reaction
Measure how fast one of the products is made
5 main factors that are important when studying rates of chemical reactions
Concentration( of solutions), temperature, surface area(for solids), catalyst, pressure (for gases)
For a reaction to occur what must reactant particles do
Collide with each other
What is the activation energy
The minimum amount of energy required for a reaction to take place
More energetic collisions allow bonds to be broken between reactant particles true or false?
True
Rates of chemical reactions are ? up if the ? of collision with greater than the activation energy ?
Speeded up, frequency, increases
If particles do not reach the activation energy what happens
They will still collide but will bounce off each other not successfully collide
Collision theory is the idea that a reaction can only occur when two particles collide together with enough energy - it has to be equal or more than the activation energy
True
What does increasing the concentration of reactants/ liquids in a solution do
It means there are more particles of reactants in the same volume which leads to more frequent and therefore successful collisions and a faster rate of reaction.
What happens when all the reactants have been used up
The reaction stops anything that was happening stops eg if acid was fizzing once all the reactants had been used up it would stop fizzing and become clear.
The reaction between calcium carbonate (marble chips) and hydrochloride acid - what two methods could be used to measure the rate of this reaction
Gas collection( product)
Mass loss (reactant)
Assessed practical how does surface area affect the rate of reaction?- tests how many cm cubed of carbon dioxide there are in (max) 180 seconds and sees how it varies between the different sizes of marble chips
The larger the surface area (to vol ratio) the higher the rate of reaction casue there are more particles so more of them to collide so more frequent successful collisions so the rate of reaction is faster
Assessed practical- how temp affects the rate of reaction between hydrochloric acid and sodium thiosulphate - add sodium thiosulphate to hydrochloric acid, and heat it at different temperatures eg: 20,30,40 etc and place it on top of a black cross and start the timer and when u can no longer see the black cross from looking straight into the solution, stop the timer
The higher the temperature the higher the reaction rate (and steeper the concentration gradient) -
Explain answer to Q 14 using collision theory
Particles move faster because of the higher temperature meaning that they will collide more frequently and they have more energy so more particles successfully collide, giving more frequent successful collisions causing a reaction.
Theory on SA and reaction rate : crushing up a solid into a powder ? its surface area to ? ratio, meaning that there is a ? area of contact between the solid and other reactant and more ? collisions, so the ? the SA of a solid the ? the rate of reaction
Increases, volume, larger, frequent, larger, faster
How to work out rate of reaction:
Pick a multiple of 10, eg: 1000, so then 1000/ time in seconds
Temperature and reaction rate theory: increasing temp of a reaction increases ? energy of the particles, meaning particles move ? And ? more frequently, also more of the collisions have energy exceeding the ? energy so more successful ? causing a ?
Kinetic, faster , collide, activation, collisions, reaction
What happens in a low temperature then
Particles don’t move as fast, less frequent collisions, less collisions exceeded activation energy so less successful collisions
Pressure and reaction rate (for gases only): Changing pressure has no effect on reactions with only ? and liquids, as the particles in these states are already ? together, but changing pressure of a reaction with ? has a similar effect to changing the concentration of a solution with ? Increadjng the ? Of a gas means there are more gas ? in a certain? Meaning they will collide more ? And rate of reaction will ?
Solids, close, gases, liquids, pressure, particles, volume, frequently, increase
How does surface area affect the rate of reaction: (what happens in the reaction with marble chips) basically :
Have a conical flask with marble chips and hydrochloric acid in the bottom with a bung and delivery tube running from there to a trough of water. in trough of water is a measuring cylinder ( secured by a clamp) full of water under which u have to put the delivery tube . What will happen is u set up all of this, put marble chips and hydrochloric acid in the bottom of the conical flask and then put the bung and delivery tube back on very quickly.
What is a catalyst?
A substance that’s speeds up a reaction without being used up
How do catalysts make reactions faster?
They provide an alternative route for the reaction with a lower activation energy
Catalysts are designed to have a large surface area true or false
True
What type of metals and metal compounds are often good catalysts?
Transition
What does the gradient of the line on a graph mean with reactions?
Measures the rate of reaction
At the start of a reaction why is the gradient so steep
Casye the reaction is at its fastest point as the reactants are at their greatest concentration
At the middle of a reaction why is the gradient less steep
More of the reactants have been used up so the concentration of reactants is lower
At the end of a reaction why is the gradient nothing
Because the reaction has stopped, so no more product is being made so it is a straight line
how big are nano particles
1-100nm in size, so roughly 1-100 * 10 to the -9
how much larger are nano particles than atoms and simple molecules?
around 100 times larger
what are nano particles used in?
Nanoparticulate materials are used in some paints, cosmetics and sunscreens
why is titanium dioxide used in sunscreen and what is the colour of it in bulk and as nano particulate
as it blocks uv light, in bulk it is white so is used in paint, but when it’s in nano particles it’s clear
what is the pro and the cons of using titanium dioxide in sun cream?
pro is it appears colourless so people can’t tell you’re wearing sun cream, doesn’t affect your appearance
cons are it clumps together so is hard to put on and as well as that it is hard to tell where you’ve applied it
what do nanoparticles being catalysts allow them to do?
- catalyse reactions more efficiently
- catalyse different reactions
- produce different products
what do self- cleaning window panes with nano particulate coatings do?
catalyse the breakdown of dirt in the presence of sunlight
if you breathe nanoparticles in or they get into your cells what are some risks?
they may catalyse reactiosn that are harmful, or toxic substances could bind to them - which could harm the body.
