C5: Rates of Reaction and Thermochemistry Flashcards
what is the rate of a reaction
the change in the concentration of the product or reactant over unit time
what are the two ways that the rate of reaction can be measured
- by measuring how quickly the reactants are used up - or measuring how quickly the product is formed
what are the 3 experimental measurements used to measure rate of reaction
- precipitation - change in mass - volume of gas given off
what type of reactions would the method of precipitation work in
- any reaction where mixing two see-through solutions produces a precipitate - which clouds the solution
what is a disadvantage of the precipitation method
- the result is subjective - different people might not agree on exactly when the mark disappears
what is a mass balance used for
measuring the rate of a reaction that produces a gas
while measuring the change in mass, how does a mass balance indicate the rate of a reaction
- during reaction, as gas is released - lost mass is easily measured on the balance - the quicker the reading on the balance drops, the faster the reaction
ho do you know when a reaction has finished in the change in mass method and why
- when the reading on the balance stops changing - because no more mass is being lost - so no more gas is being released - meaning the reaction has stopped
how can your results in the change in mass method be visually displayed
by plotting a graph of change in mass against time
what is a disadvantage of the change in mass method
- method releases gas produced into the room - if gas is harmful, safety precautions must be taken
how is the volume of gas given off in the ‘volume of gas given off’ method measured with
a gas syringe
how is a faster reaction indicated in the volume of gas given off method
- more gas is given off during a set time interval - shown by the gas syringe filling up at a quicker rate
how can you tell when the reaction has finished in the volume of gas given off method
when no more gas is produced and the gas syringe reading doesnt change
how would you plot your results on a graph from the volume of gas given off method
you would plot the graph of gas volume against time elapsed
what is a disadvantage of the volume of gas given off method
- need to be careful using youre the right size gas syringe - if reaction is too vigorous, the plunger can be blown off the end of the syringe
Give the 2 equations of how you can find the rate of reaction
- Amount of reactant used/time
- Amount of product formed/time
How can you find the rate of reaction from a graph?
The gradient
What is the relationship between rate and time?
They are inversely proportional; the faster the rate the shorter the time
What does collision theory state?
- That reactions can only occur if particles collide.
- The particles must collide with enough energy to react
- The particles must collide with the correct orientation
What is the minimum energy required for substances to react called?
Activation energy
How do the different factors increase the rate of a reaction?
Factors that increase the chance of collisions or the energy of particles
5 factors that affect rates of reaction
- Temperature
- Concentration of solutions
- Pressure of gases
- Surface area of solids
- Using a catalyst
How does surface area increase the rate of reaction?
Increasing the SA, exposes more of the surface. This means more frequent collisions in the same time and this increases the rate of reaction.
How does temperature effect the rate of reaction?
Temperature increases the speed of the particles, so they collide more often and with more energy. They also reach the activation energy required much quicker. This increases the rate of reaction
Roughly by how much will the rate of reaction will increase by if the temperature is increased by 10 degrees?
Double
How does the concentration or pressure effect the rate of reaction?
A higher concentration means more particles are dissolved in the same volume, meaning the particles are closer together and so collide more often
How do catalysts work?
They speed up reactions by lowering the activation energy of the reaction so more collisions result in a reaction.
Why can catalysts be reused?
It changes the rate of reaction but is not used up or reacts
What are the benefits of using catalysts in industrial processes?
The reduce the time and energy neede, saving money, conserve resources and reduce pollution. They can also be used again
Which group are catalysts from?
Transition metals
What are some disadvantages of catalysts?
Some are toxic and can cause harm in the environment
How does a catalyst work
They lower the activation energy as they provide an alternative pathway at a lower energy level so more successful collisions occur ^^ meaning they speed up reactions
How does a catalyst work
They lower the activation energy as they provide an alternative pathway at a lower energy level so more successful collisions occur ^^ meaning they speed up reactions
What do catalysts do and not do
They speed up reactions but are not used up
What do catalysts do and not do
They speed up reactions but are not used up
What is the meaning of a reversible reaction
A reaction that can be changed back to its original form > the reaction can go in both directions
What effect does a catalyst have on a rate of reaction
They lower the activation energy, providing a different pathway and a lower energy level so more successful collisions occur
What is the effect of temperature on rates
If increased the reactant particles move more quickly which means they have more energy and collisions happen more therefore the rate of reaction increases
What affect does the surface area have on rates of a reaction
The fate will increase as more particles are exposed to the other reactant and more collision will therefore happen
What is the mass of a substances measured with
Balance
What is the mass of a substances measured with
Balance
Whats the activation energy
The minimum energy needed for particles to react
Is bond breaking an exothermic or endothermic reaction
An endothermic reaction because energy must be supplied to break existing bonds
Is bond formation an exothermic or endothermic reaction
Exothermic reaction because energy is released when new bonds are formed
What’s the equation for energy change
Energy if bond breaking - energy if bond making
What’s the equation for enthalpy of reaction?
enthalpy of products - enthalpy of reactants
Give some facts on ammonia
It breaks down when it is heated It’s a colourless gas
How do you work out the amount of energy given out from bond making
Adding up the bond energies of all the bonds in all the products
What is a closed system
When I neither reactants nor products can enter or leave
What is the position of equilibrium
When reversible reactions reach a balance point, where the amount of reactants and the amount of products formed remain constant
What is a closed system
When I ether reactants nor products can enter or leave
When is an equilibrium reached
When the forward and reverse reactions occur at the exactly same rate
What is the position of equilibrium
When reversible reactions reach a balance point, where the amount of reactants and the amount of products formed remain constant
How is a does concentration change the position of equilibrium
If more of a reactant is added, the system would work by removing this reactant and making more of the products
How does temperature change the position of equilibrium
Decreasing the temp moves the position of E in the direction of the exothermic reaction Increasing the temp moves the position of E in the endothermic direction
How is a does concentration change the position of equilibrium
If more of a reactant is added, the system would work by removing this reactant and making more of the products
How does changing the pressure effect the post Position of equilibrium
Increasing the pressure moves the position of E to the suede with the least number of molecules
How does changing the pressure effect the post Position of equilibrium
Increasing the pressure moves the position of E to the suede with the least number of molecules
What happens if activation energy is low
Particles don’t need to collide with much energy to react Meaning they’ll react as soon as they’re mixed
What happens if activation energy is low
Particles don’t need to collide with much energy to react Meaning they’ll react as soon as they’re mixed
What can’t you do if two reactants are gases And what the alternative thing to do
Increase the concentration So you increase the pressure
How can the rate of reaction between marble chips and hydrochloride acid be changed
Changing the temperature and surface area of reactants
Why are powders like icing sugar flour and custard powder dangerous
They react very quickly as they have very large surface areas so they need to avoid naked flames
What are the pros of catalysts
Very small amounts can be used and they can be used again and again thus many industrial chemical reactions use them
What is a drawback if catalysts
They are very specific to what they can be used on
What are catalysts in living things called
Enzymes Sometimes known as biological catalysts
When do reactions stop
when one or both of the reactants are used up
What is the reactant called that causes the reactions to stop
Limiting reactant
How to measure the rate of reaction on a graph on a fine point on the graph
Make a tangent (straight line) on the curve of where the point asked is Then draw a right angles triangle and find the steepness of the tangent by dividing the height by the width Thus = vol. gas collected (divided) time taken
To measure reactions rates what do you need to do
Observe the reaction at time intervals see amount of gas released Change in mass The colour or appearance change
How to measure the rate of reaction on a graph on a fine point on the graph
Make a tangent (straight line) on the curve of where the point asked is Then draw a right angles triangle and find the steepness of the tangent by dividing the height by the width Thus = vol. gas collected (divided) time taken
what would happen if you were to increase the number of collisions or the energy with which the particles collide with
the reactions would happen more quickly
why does an increase in temperature result in an increase of rate of reaction in terms of kinetic energy
- particles are given more kinetic energy so they move faster - faster movement results in more frequent collisions with other fast moving particles
what is meant by a solution becoming more concentrated
there are more particles of reactant in the same volume
what is the word used to describe the concentration of gases in a given volume
pressure
how does breaking a solid reactant into smaller pieces affect rate of reaction
breaking a solid reactant into smaller pieces would increase the rate of reaction
even though we use a catalyst, why does the reaction equation remain the same
because a catalyst doesnt change the products of a reaction, especially because it isnt used up
if a catalyst isnt used up, how can it be effectively used in reactions
only a tiny bit needs to be used in order to catalyse large amounts of reactants
what do reaction profiles show
the energy levels of the reactants and the products in a reaction
what is a endothermic reaction
a reaction which takes in energy from the surroundings, usually in the form of heat and is usually shown by a fall in temperature of the surroundings
what is an exothermic reaction
a reaction which gives out energy to its surroundings, usually in the form of heat and usually shown by a rise in temperature of the surroundings
what can you use a reaction profile to do in terms of exo and endothermic reactions
you can use it work out if energy is released (exothermic) or taken in (endothermic)
how is an exothermic reaction shown on a reaction profile
the products are at a lower energy level than the reactants
how is an endothermic reaction shown on a reaction profile
the products are at a higher energy level than the reactants
what indicates the activation energy in a reaction profile
the difference between the reactants and the highest point on a curve
what would happen if the energy input is less than the activation energy
there wont be enough energy to start a reaction, so nothing would happen
In terms of energetics, what kind of reaction is this?
exothermic
In terms of energetics, what kind of reaction is this?
endothermic reaction
define enthalpy of solution
the heat change when 1 mol of solute completely dissolves in a solvent
define enthalpy or heat of neutralization
the heat change when 1 mol of water is produced in a neutralization reaction
define heat of combustion
the heat change when 1 mol of a compound is completely burned in oxygen
Enthalpy of formation
heat change when 1 mole of a substance is formed from its elements under standard conditions
if the temperature is given, what is the equation for enthalpy or heat of reaction
