6 Chemical reactions Flashcards
physical change
dosen’t make new chemical and are usually easy to reverse
chemical change
chemical bonds between atoms are broken and made, so the atoms get rearranged into new substances
catalyst
increases the rate of a reaction and is unchanged at the end of a reaction
(decreasesthe activation energy by providing an alternate pathway with lower activation energy)
collision theory
chemical reactions occur when the reactant particles collide with sufficient energy to react and proper orientations
effect on temperature on rate of reaction
when the temperature is increased, the particles speed increase due to higher kinetic energy. Resulting in the particles colliding more frequently. As well as having more particles that have the necessary activation energy to break bonds.
effect of concentration on rate of reaction
Doubling the concentration will also double the number of collisions. Increasing the concentration of either reactant increases the number of collisions and therefore increases the number of sucessful collisions and the reaction rate.
effect of surface area on rate of reaction
Increasing the surface area increases the frequency of collisions and reaction rate. As reactants are more exposed to the other reactants.
effect of catalyst on activation energy
a catalyst decreases the activation energy of a reaction
An investigation to measure rate of reaction using different surface areas
Method:
- dilute HCl into a conical flask
- use a delivery tube to connect this flask to a measuring cylinder upside down in a bucket of water (downwards displacement)
- add CaCO3 chips into the conical flask and quickly put the bung back into the flask
- measure the volume of gas produced in a fixed time using the measuring cylinder
- repeat with different sizes of CaCO3 chips (lumps, crushed and powdered)
redox reactions
involving simultaneous
oxidation and reduction
oxidation
loss of electrons
gain of oxygen
increase in oxidation number
reduction
gain of electrons
loss of oxygen
decrease in oxidation number
when is a reversible reaction in equilibrium
a) the rate of the forward reaction is equal to the rate of the backward reaction
b) the concentration of reactants and products are constant
When temperature increases what happens to the position of equilibrium?
Shifts the equilibrium in the direction of the endothermic reaction
When pressure increases what happens to the position of equilibrium?
Shifts the equilibrium towards the side with the fewer moles of gas
When the concentration of a substance changes what happens to the position of the equilibrium?
The equilibrium will shift to minimise the effect of the change.
- If the concentration of a reactant (on the left) is increased, the equilibrium position moves in the direction away from this reactant, and so more of the products are produced (on the right).
When a catalyst is added what happens to the position of the equilibrium?
There is no effect on the position of equilibrium. However it does allow equilibrium to be reached more quickly, or estabilished at a lower temperature, which makes reactions more profitable.
Haber Process symbol equation
N2(g) + 3H2(g) <–> 2NH3(g)
source of hydrogen in the haber process
Methane
source of nitrogen in the haber process
Air
Typical conditions of the haber process
450C, 20000 kPa/200 atm, and an iron catalyst
Source of sulfur dioxide in the contact process
burning sulfur or roasting sulfide ore
Source of oxygen in the contact process
air
typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the contact process
450C, 200kPa/2 atm and a vanadium(V) oxide catalyst
Explain, in terms of rate of reaction and position of equilibrium, why the typical conditions stated are used in the Haber process and in the Contact
process,
Temperature
low enough to achieve an acceptable yield
high enough to do this in an acceptable time
Pressure
low enough to keep costs down
high enough to achieve an acceptable yield
Acidified Potassium manganate (VII) purpose
Acidified potassium manganate (VII) is an oxidising agent.
- from purple to colourless
Aqueous potassium iodide purpose
Aqueous potassium iodide is a reducing agent
- from colourless to yellow-brown
observations of NO2
brown gas and pungent smell
