6. Chemical Reactions Flashcards
Equilibrium
The state achieved when the forward and reverse reactions occur at the same rate and the concentration of the reactants and products stay constant.
Is White copper sulfate powder turning blue when water is added and white again when water is evaporated a chemical or physical reaction
Physical
How can compounds be split up
chemical separating techniques such as electrolysis
Difference between chemical and physical changes
In a physical reaction, the substance itself doesn’t change, only the form. E.g. changes of state
In a chemical reaction reactants are converted to products and have different properties
Physical changes are reversible, most chemical changes aren’t e.g. combustion
What factors affect the rate of reaction (5)
Concentration
Pressure (only in gases)
Temperature
Catalyst
Surface area
rate of reaction
The change in concentration per unit time of either the product or the reactants
What is the formula for gases
v=n24
How does concentration affect the rate of reaction
The higher the concentration the higher the number of particles per unit volume, resulting in more effective collisions per unit time and a faster reaction rate
How does temperature affect the rate of reaction
As the temperature increases, the particles gain energy and move faster, resulting in more effective collisions per second with sufficient energy to react
How does a catalyst affect the rate of reaction
By introducing a catalyst it lowers the activation energy resulting in a higher rate of effective collisions per second as more molecules collide with equal or greater activation energy.
How does surface area affect the rate of a reaction
The smaller the particles size(the greater the surface area), the more surface exposed for reactions to take place, therefore there are more effective collisions per unit time.
How does pressure affect the rate of reaction
Reducing the volume of the container means that you are reducing the space in which the gas particles can move, therefore more effective collisions per unit time.
How can we measure the rate of a reaction
- Measuring the volume of gas given off every minute
- Measure the decrease in mass as the gas escapes
How is nitrogen obtained
Distillation of liquid air
How is hydrogen obtained
Methane
What effect does equilibrium have on the concentration of the reactants/products in a reaction
None, they cancel each other out
Homogeneous equilibrium
One in which all species present are in the same phase
E.g gas-phase/solution reactions
Heterogeneous equilibrium
One in which the reactants, products, or both are in more than one phase
E.g reactions involving solids and gases or solids and liquids
What are the characteristics/requirements of equilibrium
Constant concentration of reactants and products given there is no other change in the system
Dynamic-products and reactants changing into each other by chemical reactions constantly and at the same time
Must occur in a closed system so nothing can escape
How does a catalyst effect equilibrium
It affects the rate of a reaction, but has no influence on the equilibrium of a reaction
What factors affect equilibrium (3)
Temperature
Pressure (only in gasses)
Concentration
What is the Haber process
The industrial process used to make ammonia
What are the uses of ammonia
Nitric acid-cleaning products
Explosives
Fertilizers
How is nitrogen gas obtained
From fractional distillation
How is hydrogen gas obtained
Through cracking of natural gases
Do you make or break bonds when making ammonia, therefore what is the forward reaction of ammonia
Make bonds
Exothermic
What is the equation for the haber process
N2(g) + 3H2(g) <->2NH3(g)
What will a system do to try to increase pressure
It will shift in the direction of the most gas molecules
What are the conditions of the harbour process and what do they do (3)
Iron catalyst-does not take part in the reaction, just facilitates it. It increases the rate of the reaction by lowering the activation energy
Temperature-450*, it is low enough to favour the forward reaction, but high enough that the rate is economical-can’t be too low otherwise rate of reaction would be too slow
Pressure-200atm/20 000kPa, high enough is needed to favour forward reaction, but not too high as maintaining pressure is very costly
What are the uses of sulfuric acid (2)
Manufacture of paint
Car batteries
What is significant about the steps in the contact process
Only the second one is reversible
How do they stop toxic gases released during the contact process from being released into the atmosphere
The chimneys are fired with acid scrubbers, bases Eg.(Na2CO3)
Or by recycling gases between stage 2 and 3
Major source of sulfuric
Crude oil/petroleum/fossil fuels
Uses of sulfur dioxide (2)
Bleaching of wood fibres to make paper
Food preservatives
contact process conditions + reasons
450* Celsius - a lower temperature doesn’t produce an economical rate of SO3 and it would slow the reaction
200 kPa/2 atm pressure- high enough that equilibrium shifts in direction of lesser gas yield, low enough to be economical
Vanadium (V) oxide catalyst V2O5 - to increase the rate of reaction
Why can water not be directly reacted with sulfur trioxide
It is too volatile and a toxic gas is produced
State 2 characteristics of an equilibrium
The rate of the forward reaction = rate of reverse reaction
Concentration of reactants and products are constant
Sources of hydrogen and nitrogen in the harbour process
Methane (cracking of natural gases)
Fractional distillation of Air
Haber process conditions (3)
450*C
Iron catalyst
20 000 kPa/ 200 atm
Sources of sulphur dioxide and oxygen in the contact process
Roasting sulphur ores
Air
Contact process equation
2SO2(g) + O2(g) ->REVERSIBLE<- 2SO3(g)
How the addition of water to anhydrous compounds can change the direction of a reversible reaction
When anhydrous compounds are exposed to water, they can undergo a hydration reaction and become hydrated. This can shift the equilibrium of the reaction towards the products. However, if water is removed from the system, it can cause the hydrated compound to become anhydrous again, and shift the equilibrium towards the reactants.
copper(II) sulfate - White- blue
cobalt(II) chloride - blue - pink
How the effect of heat on hydrated compounds can change the direction of a reversible reaction
When hydrated compounds are heated, the water molecules that are bound to the compound can be released, causing the compound to become anhydrous. This can shift the equilibrium of the reaction towards the products. On the other hand, if the hydrated compound is cooled, it can cause the water molecules to rebind with the compound, shifting the equilibrium towards the reactants.
Copper (II) sulphate - blue - white
Cobalt (II) chloride - pink - blue
How to identify redox reactions when using acidified potassium manganate (VII)
KMnO4 is an oxidising agent which turns from purple to colourless when added to a reducing agent containing solution
How to identify redox reactions when using Potassium iodide (KI)
KI is a reducing agent which when added to an acidified oxidising agent containing solution such as Cl(aq) or hydrogen peroxide (H2O2) turns the solution red-brown due to the formation of iodine
