Chem q Flashcards
Explain how the abundance of an isotope is measured.
Detector, Current related to abundance
Catalyst
Increases rate of chemical reaction without being used up
Along period 2, which element deviates in the trend in ionisation energy and why?
Oxygen, as it has electron pair in the p orbital so repulsion occurs.
What element in period 2 has the highest 2nd ionisation energy?
Lithium
What is a dynamic equilibrium?
Where rates of forwards and backwards reactions are the same. Concentrations are constant.
What is Hess’s law?
That the enthalpy change of a reaction at constant pressure is independent of the route taken.
H2C=CH2(g) + H2O(g) CH3CH2OH(g)
Identify the catalyst used in this reaction
H3PO4 or H2SO4
Write an equation, including state symbols, for the reaction that has an enthalpy change that is the standard enthalpy of formation of ethanol.
2C(s) + 3H2(g) + ½O2(g) —> CH3CH2OH(l)
Suggest why the experimental value is different from data book value.
Mean bond enthalpies are an average from a range of compounds
State why the standard enthalpy of formation for oxygen gas is zero.
It is an element
Define enthalpy of solution.
Enthalpy change when 1 mole of solid dissolves completely in water to give a solution of infinite dilution at constant pressure.
Define enthalpy of hydration.
Enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution. Hydration enthalpies are always negative.
Give two features of a reaction at equilibrium.
- Concentrations stay constant
- Forward rate = backward rate
Why does a catalyst have no effect on equilibrium?
Speeds up reaction on both sides, increases rate.
Define mean bond enthalpy.
Enthalpy needed to break a bond, averaged over different molecules.
Define enthalpy of formation
enthalpy change when one mole of a compound is formed from its elements in their standard states
Why does gibbs free energy change for the formation of Nitrogen monoxide stay constant at different temperatures?
N2 + O2 → 2NO
Number of molecules is the same of either side. So entropy stays constant.
Enthalpy of lattice formation
Enthalpy change when one mole an ionic substance is formed from its ions in gaseous state.
Explain the interactions between water molecules when F- becomes hydrated.
Water is polar and positive H are attracted by F– ions
Why is pure water not acidic?
[H+] = [OH–]
Buffer solution
Maintains a constant pH, despite the addition of small amounts of acid or alkali.
