Topic 7: Rates of Reaction and Energy Changes Flashcards
What does rate of reaction mean?
How quickly a reaction happens
What are the 2 ways that rate of reaction can be calculated?
- rate of reaction = amount of product formed/time
OR - rate of reaction = amount of reactant used/time
What are the common units of rate of reaction?
g/s
cm3/s
mol dm3/s
What are the 3 ways to measure rate of reaction?
- Time it takes for the reactants to form a precipitate
- The change in mass over time (mass after reaction - mass before reaction)
- Volume of gas produced over time
What goes on the x axis and on the y axis of a rate of reaction graph?
Y axis - amount of product formed
X axis - time
What does a steep line show on a rate of reaction graph?
A faster rate of reaction
(The steep the line, the faster the rate of reaction)
What do flat lines show on a rate of reaction graph?
The reaction has finished
If more reactant is used in a reaction, how does it affect how much product is formed?
The more reactants used, the more products formed
How can you find the rate of reaction on a rate of reaction graph?
The gradient
How to calculate gradient?
Gradient = change in y/change in x
OR
Gradient = rise/run
What’s the process to find the rate of reaction at a specific point (if it’s on a curve) on a rate of reaction graph?
- Draw a tangent to the curve at that point
- Then create triangle in dotted lines - to find the gradient
What are the 4 factors affecting rates of reaction?
- Temperature
- Pressure or concentration
- Surface area
- Catalysts
What is activation energy?
The minimum amount of energy that particles need to react
What 2 things does rate depend on with collision theory?
Collision frequency - the more collisions between particles, the faster the rate of reaction
&
Collision energy - the more collisions with at least the activation energy, the faster the rate of reaction
If there is high energy and high frequency when particles collide, what happens to the rate of reaction?
The rate of reaction is fast
If there is low energy and low frequency when particles collide, what happens to the rate of reaction?
The rate of reaction is slow
If a reaction is done at a high temperature, what happens to the rate of reaction? Why?
The rate of reaction is fast - particles move faster - collide more frequently with more heat energy
If the reaction is done at a cold temperature, what happens to the rate of reaction? Why?
The rate of reaction is slow - particles move slower - collide less frequently with less heat energy
If the reaction is done at a high pressure or concentration, what happens to the rate of reaction? Why?
The rate of reaction is fast - the more particles in the same volume, the more frequent the collisions
If the reaction is done at a low pressure or concentration, what happens to the rate of reaction? Why?
The rate of reaction is slow - the less particles in the same volume, the less frequent the collisions
If the reaction has particles with a small surface area in the reaction, what happens to the rate of reaction? Why?
The rate of reaction is fast - more area for particles to collide with - more frequent collisions
If the reaction has particles with a large surface area in the reaction, what happens to the rate of reaction? Why?
The rate of reaction is slow - less area for particles to collide with - less frequent collisions
As size of particles in a reaction decreases, what happens to the surface area to volume ratio?
The surface area to volume ratio is larger - less surface area of particles within a large volume
What is a catalyst?
Speeds up a reaction without being chemically changed or used up in the reaction, and without changing the products
What happens to activation energy when a catalyst is used in a reaction? Why?
It’s lower - allows more collisions to have energy to react with each other - increases rate of reaction
What is an example of a catalyst? What’s a use for it?
An enzyme - used to make alcoholic drinks
What 2 types of energy transfers are there?
- Endothermic reaction
- Exothermic reaction
What is an endothermic reaction?
A reaction that takes in heat energy from the surroundings
What is an endothermic reaction shown by?
A decrease in temperature
What is an exothermic reaction?
A reaction that gives out heat energy to the surroundings
What is an exothermic reaction shown by?
An increase in temperature
What equipment is used during the measuring of a temperature change?
- A thermometer - to measure the temperature
- Large beaker with a polystyrene cup (with reaction mixture in it and a lid on it) in it
- Cotton wool around the polystyrene cup - to insulate it
How can temperature change be measured?
- Record initial temperature
- Record maximum temperature reached
- Then do: maximum temperature reached - initial temperature
What 2 things can the polystyrene cup method, that measures temperature change, be used for?
- Dissolving salts in water
- Neutralisation, displacement and precipitation reactions
What does the reaction profile of an endothermic reaction look like (talk about: activation energy, energy of reactants and energy of products)?
Activation energy: high
Energy of reactants: low
Energy of products: high
If a reaction profile shows a reaction where the PRODUCTS HAVE MORE energy than the reactants, what type of reaction is it? Has energy been absorbed or released?
Endothermic reaction - energy has been absorbed
What does the reaction profile of an exothermic reaction look like (talk about: activation energy, energy of reactants and energy of products)?
Activation energy: low
Energy of reactants: high
Energy of products: low
If a reaction profile shows a reaction where the REACTANTS HAVE MORE energy than the products, what type of reaction is it? Has energy been absorbed or released?
Exothermic reaction - energy has been released
Do endothermic reactions break or form bonds?
They break bonds
Do exothermic reactions break or form bonds?
They form bonds
What is an example of an endothermic reaction?
Photosynthesis
Why do endothermic reactions break bonds?
Because energy used to break bonds is greater than energy released by forming new bonds in endothermic reactions
Why do exothermic reactions form bonds?
Because energy released by forming bonds is greater than energy used to break existing bonds in exothermic reactions
How can overall energy change be calculated?
Overall energy change = total energy needed to break bonds - total energy released by forming bonds
