Rates Of Reaction Flashcards
What is rate of reaction?
The speed at which a reaction takes place - it does not increase or decrease the amount of produce made
How can rate of reaction be observed?
My measuring how quickly the reactants are used up or how quickly the produces are formed
What happens to the rate of reaction over time?
Rate of reaction will decrease as reactants are used up. Eventually it will be presented as a straight horizontal line which represents all reactants being used up.
What us the equation for rate of reaction?
Amount of reactants used or amount of product formed/ time
What are the different ways rate if reaction can be measured?
- precipitation
- change in mass
- volume of gas given off
What must particles do in order to react?
Collide with enough energy (the minimum energy needed is called the activation energy)
-the more often reactants collide, the more successful collisions there are and so the faster the reaction is.
How does increasing temperature increase rate of reaction?
When the temperature is increases the particles move faster (more kinetic energy) so there are more collisions. Temperature also increases the energy of the collisions as particles are moving faster so collisions are more successful
How does increasing concentration/pressure increase rate of reaction?
If a solution is more concentrated it means there are more particles of reactants in the same volume so collisions are more likely.
In a gas increasing pressure means particles are more crowded so collisions are more frequent
How does smaller solid particles/ more surface areas result in a higher rate of reaction?
If one reactant is solid, breaking it into smaller pieces will increase its surface area to volume ratio. This means particles around it will have more area to work on so collision frequency increases
What is a catalyst?
A substance which increases the rate if reaction without being chemically changed. It won’t change the products if the reaction
How does a catalyst work?
By decreasing the activation energy needed for the reaction to occur by providing an alternative reaction pathway that has lower activation energy
-this means more particles have the minimum amount of energy so will collide more frequently
What do reaction profiles show?
The energy levels of the reactance and the products in a reaction. You can use them to work out if energy is released or taken in
What is an exothermic reaction?
An exothermic reaction is one which gives out energy to the surroundings (usually in the form of heat and usually shown in a rise in temperature of the surroundings)
What is an endothermic reaction?
One which takes in energy from the surroundings (usually in the form of heat and usually shown by a fall in the surrounding temperature)
What do exothermic reaction profiles show?
- the products are at a lower energy than the reactants as more energy is released in making bonds than breaking bonds.
- the horizontal lines represents the energy stored in the bonds
What do endothermic reaction profiles show?
- the products are at a higher energy than the reactants as more energy is needed to break the bonds then is released by new bonds made
- the difference in height represents energy taken in during the reaction
How is activation energy represented on a reaction profile?
It’s the energy difference between the reactants and the highest point on the curve
What does a change in temperature depend on ?
The reagents used
-combustion, dissolving salts in water, neutralisation, displacement and precipitation reactions all tend to be exothermic but there are exceptions
Is it easier for metals to react with steam or water?
Steam because they have a lot more energy as are a gas and so travel faster. This means successful collisions are more likely and more frequent
How do we represent a faster rate of reaction on a graph?
Steeper gradients
-yet if there are multiple lines they must finish at the same point as rate of reaction does not affect the amount of produce made
What is the formula for measuring bond energy?
Reactants minus products
If results are positive when measuring bond energy what type of reaction is it?
Endothermic as more energy was needed to break than released by making new bonds.
If results are negative when measuring bond energy what type of reaction is it?
Exothermic as more energy was released by making new bonds than needed to break reactants bonds
What is a reversible reaction?
When reactants form products which can react together to form the reactants again
A + B = C + D
What happens to a reversible reaction overtime?
It would reach an equilibrium. This is because the forward reaction eventually slows down as their concentration falls and the backwards reaction would speed up as the produce concentration would speed up -so their rates would soon equal out
What is the effect if an equilibrium?
Both reactions are still happening but there is no overall effect as the concentration and rate of the forward and backward reaction are equal -dynamic equilibrium
What must the conditions be for a dynamic equilibrium to occur?
It must happen in a closed system so no other factors are influencing it and none of the reactants and products can escape
What is le chatelier’s principle?
It states that if you change a reaction condition, the equilibrium will shift to oppose and counteract that change
How does concentration effect equilibrium?
Adding more molecules so either side of the reaction will cause a shift in the opposite direction as the reaction will want to oppose this change
-decreasing the concentration will have the opposite effect
How does pressure effect equilibrium?
(Only effects gases)
If you increase the pressure the equilibrium will move towards the side that has fewer moles of gas to reduce pressure
If you decrease the pressure the equilibrium will more towards the side that has more moles of gas to increase pressure
How does temperature effect equilibrium?
- increasing the temperature always favours the endothermic reaction to absorb extra heat
- decreasing the temperature always favours the exothermic reaction to produce more heat
What was the background behind the Haber process?
- in 1900s farmers main source of nitrogen compounds used for fertilisers from sodium nitrate in Chile was running out so people turned to the air as a source
- fritz haber to 4 years to perfect the conditions needed to make ammonia in 1908 by studying the reaction between hydrogen and nitrogen as nitrogen was very unreactive so hard to convert to ammonia
What is the haber process reversible reaction equation?
Nitrogen + hydrogen— ammonia
N2 (g) + 3H2 (g) — 2NH3 (g
What are the perfect conditions for the haber process?
- The perfect conditions for the highest yield are high pressures and low temperature
- yet a compromise of 200atm and 450° is used because too high pressure is expensive and potentially dangerous. Too low of a temperature slows the rate if reaction. The compromise makes it profitable
- iron is used as a catalyst to make the reaction go faster but doesn’t affect the equilibrium position of percentage yield
What is the equation to make ammonium sulphate which is used as a fertiliser to provide essential minerals for plants ?
Ammonia + sulphuric acid — ammonium sulfate
NH3 (aq) + H2SO4 (aq) — (NH4)SO4 (aq)
What are uses of ammonia?
- Nitrogen fertilisers which contain Soluble nitrogen compounds
- cleaning fluids and chemicals
- floor waxes
- hair dye
What is the factors of creating ammonia sulphate in a lab?
- ammonia is got from previously prepared bottles
- equipment used is a lot more simple such as lots of glass wear and a burette as temperatures and pressures are low
- much safer so simple safety equipment such as goggles
- method is slow and simple so small batches are made so leads to dried crystals being made
- both reactants are Soluble so a titration method is used and methyl orange indicator
What are the factors of creating ammonia sulphate in industry?
- ammonia comes from the haber process so uses raw materials
- strong metal equipment is used to withstand the big pressures and high temperatures
- safety is more rigid due to the potential danger
- method is quicker and continuous leading to the creation of pellets in batches
