Chemical reactions Details Flashcards
Signs of a chemical change
-One or more new chemical substances are formed
-Energy is taken in/given out during the reaction
-Change is usually difficult to reverse
Signs of a physical change
-No new chemical substances are formed
-Change is usually easy to reverse
Factors which affect the rate of reaction
-Concentration
-Pressure
-Temperature
-Surface area(of reactants)
-Presence of catalyst
Why increased concentration increases the rate of reaction
-More particles per unit volume
-Higher collision rate
-Higher rate of reaction
Why increased pressure affects the rate of reaction
-Gas molecules are closer together
-Increased collision rate
-Increased rate of reaction
Why increased temperature affects the rate of reaction
-Particles have more energy and move faster
-Increased collision rate
-More particles have enough energy to start a reaction
-Increased rate of reaction
Why increased surface area affects the rate of reaction
-More particles exposed to other reactant
-Greater chance of particles colliding
-Increased collision rate
-Increased rate of reaction
Features of catalysts
-Increase the rate of reaction
-Is unchanged at the end of the reaction
-Decrease the activation energy of a reaction
A reversible reaction in a closed system is at equilibrium when…
-the rate of the forward reaction is equal to the rate of the reverse reaction
-the concentrations of reactants and products are no longer changing
Factors which affect the position of equilibrium(in a reversible reaction)
-Changing temperature
-Changing pressure
-Changing concentration
-Removing the product
Effect on yield if temperature is increased in a reversible reaction(forward reaction is exothermic)
temperature ↑ means yield ↓
Effect on yield if temperature is increased in a reversible reaction(forward reaction is endothermic)
temperature ↑ means yield ↑
If the pressure is increased(in a reversible reaction), the equilibrium moves…
in the direction of the fewest molecules of gas
When does a change in temperature shift equilibrium?
ALWAYS
When does a change in pressure shift equilibrium
When the reactants/products are gases and the number of molecules is different on each side of the equation
The Haber process is used for the…
production of ammonia
Symbol equation for the Haber process
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
Where hydrogen needed for the Haber process is obtained from
Methane
Where nitrogen needed for the Haber process is obtained from
Air
Typical conditions for the Haber process
-Temperature: 450°C
-Pressure: 20,000kPa/200atm
-Catalyst: iron
The Contact process is used for the…
production of (concentrated)sulfuric acid
Symbol equations for the Contact process
2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
H₂O(l) + SO₃(g) → H₂SO₄(l)
Where sulfur dioxide needed for the Contact process is obtained from
-Burning sulfur
-Roasting sulfide ores
Where oxygen needed for the Contact process is obtained from
Air
Typical conditions for the Contact process
-Temperature: 450°C
-Pressure: 200kPa/2atm
-Catalyst: vanadium(V) oxide
The temperature for the Haber/Contact process is chosen as it is…
-low enough to achieve an acceptable yield
-high enough to do this in an acceptable time
The pressure for the Haber/Contact process is chosen as it is…
-low enough to keep costs down
-high enough to achieve an acceptable yield
Potassium manganate(VII) is an(in terms of redox)…
oxidising agent
Use of potassium(VII) manganate
Used to test for the presence of reducing agents
In the presence of a reducing agent, the colour of potassium manganate(VII) changes…
from purple to colourless
Potassium iodide is(in terms of redox)…
a reducing agent
Use of potassium iodide
Used to test for the presence of oxidising agents
When potassium iodide is added to an acidified solution of an oxidising agent(eg. hydrogen peroxide(H₂O₂), aqueous chlorine), the colour of the solution changes…
from colourless to brown(due to the formation of iodine(I₂)
