Chemistry: Transition Metals Part 3
This flashcard set explains the function and impact of catalysts in chemical reactions, including how they lower activation energy and increase reaction rates. It also highlights why transition metals are effective catalysts and defines heterogeneous catalysis based on phase differences.
Catalyst
Substance which increases rate of a chemical reaction without being changed in chemical composition/amount
Key Terms
Catalyst
Substance which increases rate of a chemical reaction without being changed in chemical composition/amount
What do catalysts provide
An alternative reaction route with a lower activation energy
What is not changed in presence of a catalyst
Delta H
Why does rate of reaction increase in presence of a catalyst (MB)
Shaded area bigger- more molecules have energy greater than or equal to activation energy- more successful collisions
Why can transition metals act as catalysts in a wide range of reactions
They have variable oxidation states
Heterogeneous catalyst
A catalyst in a different state/phase to the reactants
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| Term | Definition |
|---|---|
Catalyst | Substance which increases rate of a chemical reaction without being changed in chemical composition/amount |
What do catalysts provide | An alternative reaction route with a lower activation energy |
What is not changed in presence of a catalyst | Delta H |
Why does rate of reaction increase in presence of a catalyst (MB) | Shaded area bigger- more molecules have energy greater than or equal to activation energy- more successful collisions |
Why can transition metals act as catalysts in a wide range of reactions | They have variable oxidation states |
Heterogeneous catalyst | A catalyst in a different state/phase to the reactants |
Examples of heterogeneous catalysts |
- vanadium (V) oxide in contact process |
Why is a very thin layer of metal used on a support medium when transition metals act as catalysts |
|
How to heterogeneous catalysts work | By adsorbing reactants to active sites on catalyst surface |
How can heterogeneous catalysts be poisoned | Impurities in reactants May also bind to active sites and block reactants |
Why does catalyst being poisoned reduce efficiency of catalyst | It blocks active sites and reduced SA available for reaction- slowing it down |
How can poisoning of catalyst be minimised | Purifying the reactants |
What is the contact process used industrially for | To manufacture sulphuric acid |
What acts as a heterogeneous catalyst in contact process | Vanadium (V) oxide |
Step 1 contact process; | Sulfur dioxide diffuses onto active sites and redox reaction occurs |
Reaction for oxidation of sulfur dioxide to sulfur trioxide by vanadium 5 oxide | V2O5 + 5O2 > V2O4 + SO3 |
Step 2 contact process | Vanadium 4 oxide reacts with oxygen to regenerate vanadium 5 oxide |
Equation vanadium for oxide and oxygen to vanadium 5 oxide | V2O4 > 1/2O2 > V2O5 |
Overall equation contact process | SO2 + 1/2 O2> SO3 |
Homogeneous catalyst is | A catalyst in the same state/phase as the reactants |
Why may reaction between peroxodisulfate ions and iodide ions be slow | Reactants have same charge and so are less likely to collide |
What may be use to catalyst me reaction of peroxodisulfate ions with iodide ions | Iron 2/3 |
Step 1 catalysis iodide and peroxodisulfate with iron 2 | 2Fe2+ + S2O82- > 2SO42- + 2Fe3+ |
Step 2 catalysis iodide and peroxodisulfate with iron 2 | 2Fe3+ + 2I- > I2 + 2Fe2+ |
Intermediate species in catalysis of iodide peroxodisulfate with iron 2 | Iron 3 |
Why is iron 3 just as effective in catalysing this reaction as iron 2 | Step 2 could occur before step 1 |
Why is reaction between manganate 7 ions and ethanedioate ions initially very slow | Many reactants, both negative |
When does the rate of the reaction between manganate 7 and ehtanedioate ions increase rapidly | As conc of Mn2+ produced increases |
What does the Mn2+ act as in reaction between manganate 7 and ethanedioate | An auto catalyst |
Autocatalysis | When the catalyst for the reaction is a reaction product |
Step 1 autocatalysis manganate 7 and ethanedioate | 2MnO4- + 5C2O42- + 16H+ > 2Mn2+ + 8H2O + 10CO2 |
Step 2 autocatalysis | 4Mn2+ + MnO4- + 8H+ > 5Mn3+ + 4H2O |
Step 3 autocatalysis | 2Mn3+ + C2O42- > 2CO2 + 2Mn2+ |
Intermediate species in autocatalysis | mn3+ |