OCR A-Level Chemistry: Module 5 - Physical Chemistry and Transition Elements
This flashcard set explains why complex reactions occur in multiple steps, defines half-life, and shows how concentration-time graphs reveal reaction order. It also confirms that the half-life of a first-order reactant remains constant regardless of concentration changes.
A proposed mechanism for a reaction takes place in several steps. Suggest two reasons why the reaction couldn’t take place in one step (2)
Stoichiometry in rate equation does not match stoichiometry in overall equation
Collision unlikely with more than 2 ions/species/particles
Key Terms
A proposed mechanism for a reaction takes place in several steps. Suggest two reasons why the reaction couldn’t take place in one step (2)
Stoichiometry in rate equation does not match stoichiometry in overall equation
Collision unlikely with more than 2 ions/species/particles
What is meant by the half life of a reaction? (1)
Time for concentration of reactant to fall to half of the original value
How can a concentration against time graph for a reactant be used to work out order of reaction? (2)
Show two half-lives on graph
Zero - half life decreases
First - half life is constant
Second - half life increases
If concentration is altered, is the half life effected on a first order reactant? (1)
No
What effect on Kc does using a smaller container for the reaction have? (1)
No effect
What effect does adding a catalyst have on Kc? (1)
No effect
Related Flashcard Decks
Study Tips
- Press F to enter focus mode for distraction-free studying
- Review cards regularly to improve retention
- Try to recall the answer before flipping the card
- Share this deck with friends to study together
| Term | Definition |
|---|---|
A proposed mechanism for a reaction takes place in several steps. Suggest two reasons why the reaction couldn’t take place in one step (2) | Stoichiometry in rate equation does not match stoichiometry in overall equation |
What is meant by the half life of a reaction? (1) | Time for concentration of reactant to fall to half of the original value |
How can a concentration against time graph for a reactant be used to work out order of reaction? (2) | Show two half-lives on graph |
If concentration is altered, is the half life effected on a first order reactant? (1) | No |
What effect on Kc does using a smaller container for the reaction have? (1) | No effect |
What effect does adding a catalyst have on Kc? (1) | No effect |
State three large scale uses of hydrogen (3) | Choose three from: Extraction of some metals from ores Fuel cells Hydrogenation of alkenes Haber process Making HCl Making methanol |
The forward reaction is exothermic, if the temperature is raised, what effect is there on Kc? (1) | Kc is smaller |
2 mols LHS, 2 mols RHS, if pressure is increased, what effect is there on Kc? (1) | Kc is same Kc is not changed by pressure |
4 mols LHS, 3 mols RHS, forward reaction exothermic. A chemist increases the temperature and pressure, explain why it can be difficult to predict the change to equilibrium position (2) | Increased temperature shifts to the left |
| Proton donor |
Define weak acid (1) | Partially dissociates |
What name is given to Kw? (1) | Ionic product of water |
What is the expression for Kw? (1) | Kw = [H+(aq)] [OH–(aq)] |
What is meant by the rate-determining step? (1) | The slowest step |
What information is provided by Ka values? (1) | Strength of acid |
H2PO4(-) can act as an acid or a base. Why can Ca(H2PO4)2 in water act as a buffer solution, using equations? (3) | H2PO4- produced from Ca(H2PO4)2 |
State what is meant by a buffer solution (1) | A solution that minimises pH changes |
Suggest a chemical that could be added to methanoic acid to prepare a buffer solution. Explain (2) | HCOONa Supplies HCOO(-) |
What factors determine the pH of a buffer solution? (2) | Ka Temperature |
Write an equation for the reaction of nitric acid with limestone (2) | 2HNO3 + CaCO3 -> Ca(NO3)2 +CO2 + H2O |
Why is the pH scale a more convenient measurement for measuring acid concentrations than [H+]? (1) | pH makes numbers manageable |
Define a strong acid (1) | Completely dissociates |
A solution mixes NaOH and CH3COOH (less moles of NaOH than CH3COOH), why is it a buffer solution? (2) | Solution is a mixture of CH3COOH and CH3COONa Has an excess of acid |
A solution mixes NaOH and CH3COOH (same number of moles), why is it not a buffer solution? (2) | Contains only CH3COONa | Therefore it's neutral |
The pH of water at 25°C is 7.0, and 6.7 at 40°C. What does this show about water's tendency to ionise with temperature? (2) | [H+] increases |
Why is second electron affinity an endothermic process? (2) | Negative ion repels electron being added |
Suggest why the entropy of water is zero at 0K (1) | Particles are in maximum state of order |
Why is the entropy change of liquid to gas, bigger than that of solid to liquid? (2) | Increase in disorder is bigger |
Define feasible reaction (1) | ΔG =< 0 |
Why might a reaction be feasible at all temperatures? (3) | ΔG=ΔH-TΔS |
2SO2(g) + O2(g) 2SO3(g) | Why is there a decrease in entropy of the system? (2) | Fewer moles of gas | More order in system |
State what is meant by enthalpy change (2) | Internal energy change measured at constant pressure |
How is entropy changed when water freezes and why? (1) | Decreases | State changes to more ordered one |
Define lattice enthalpy (2) | The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions |
Describe and explain the factors that affect the values of lattic enthalpies (3) | Decreases in ionic size makes it more negative |
Why is enthalpy change of hydration of chloride ions exothermic? (1) | Hydration involves bond forming |
Explain why enthalpy change of hydration of Mg ions is more exothermic than Ca ions (2) | Magnesium ion is smaller | Mg2+ has a stronger attraction to H2O |
Define enthalpy change of solution (2) | The enthalpy change that takes place when one mole of a solute dissolves in a solvent |
Define enthalpy change of hydration (2) | The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions |
Define standard entropy (2) | The entropy of one mole of a substance, under standard conditions |
Discuss two advantages and two disadvantages of using fuel cells for energy rather than using fossil fuels (4) | Advantages: Only H2O formed Greater efficiency Disadvantages: H2 difficult to store H2 difficult to manufacture initially |
Define standard electrode potential (3) | Emf of electrochemical cell comprising a half cell combined with a standard hydrogen electrode at 1 atm, 298K and solutions of 1 mol/dm^3 |
Give one use of chromium metal and state the property that makes it suitable (1) | Stainless steel | Corrosion resistance |
When given the cell potentials of redox systems, how can the most powerful oxidising agent be identified? (1) | LHS of most positive cell potential |
What is used for the electrode and solution in the H2 half cell? (2) | Platinum electrode | H+ at 1 mol/dm^3 |
What is the direction of electron flow in a cell circuit? (1) | Most positive solution to most negative solution, along the wire |
Define transition element (1) | Has at least one ion with a partially filled d-orbital |
Define complex ion (1) | A central metal ion surrounded by ligands |
Define ligand (1) | Molecule with a lone pair(s) of electrons capable of forming dative bonds to a metal ion |
NaOH(aq) is added to Fe2+(aq), what would be observed, and what is the ionic equation? (2) | Green precipitate |
In octahedral complex ions, what kind of stereoisomerism is shown? (1) | Optical and geometric isomerism |
In square planar complex ions, what kind of stereoisomerism is shown? (1) | Geometric isomerism |
In tetrahedral complex ions, what kind of stereoisomerism is shown? (1) | Optical isomerism |
Which reagent should be chosen for converting [Ru(H2O)6]3+ to [Ru(H2O)5Cl]2+? (1) | Concentrated HCl |
What name is given to changing the molecules that form dative covalent bonds with metal ions? (1) | Ligand substitution |
How is the end point of a titration involving iodine identified? (1) | Starch added is decolourised |
Suggest why a cyanide ion can act as a ligand (1) | Has a lone pair of electrons that can be donated |
NaOH(aq) is added to Fe3+(aq), what would be seen and write an ionic equation (2) | Brown precipitate |
Define bidentate ligand (2) | Ligand able to donate two lone pairs to form dative covalent bonds |
Describe a test to show the presence of Fe3+ ions in a solution of FeSO4.7H2O (1) | Adding NaOH(aq) will give a brown precipitate |
[Cu(H2O)6]2+ is reacted with conc HCl, describe the observations made (1) | Blue to yellow solution |
Describe the bonding within [CuCl4]2– (2) | Lone pair on chloride ions donated to copper(II) ion |
Define co-ordination number (1) | Number of dative covalent bonds formed with the transition metal |
How does cisplatin help with cancer treatment? (2) | Binds with DNA | Prevents tumour growth |
State two typical properties of compounds of a transition element (2) | Form complexes | Act as catalysts |
Explain why the H-O-H bond angle in a water ligand is 107 not 104.5 (3) | Water molecule 2 lone pairs and 2 bond pairs |
Which metals are present in brass? (1) | Copper and zinc |
Give a common use for brass and state the property responsible (1) | Coins | Corrosion resistance |