M3S2: Physical Chemistry

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17 Terms

1
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Standard condition

  • 100kPa

  • 298K

2
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Standard enthalpy change of reaction

  • ΔrH

  • Enthalpy change when reaction occur in molar quantities shown in chemical equation, under standard conditions & standard state

3
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Standard enthalpy change of formation

  • ΔfH

  • Enthalpy change when 1 mole of compound formed from its elements in their standard states

4
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Standard enthalpy change of combustion

  • ΔcH

  • Enthalpy change when 1 mole of substance completely burn in oxygen under standard conditions & standard states

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Standard enthalpy change of neutralisation

  • ΔneutH

  • Enthalpy change when solution of acid & alkali react = 1 mole water under standard conditions

6
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Measuring enthalpy change equation

  • q = mcΔT

  • c = 4.18

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Effect of temp on reaction rate

  • Increase temp = molecules on average have more Ek therefore greater proportion of molecules will have at least activation energy required to react

  • For Boltzmann, same num molecules = area under graph same

<ul><li><p>Increase temp = molecules on average have more E<sub>k</sub> therefore greater proportion of molecules will have at least activation energy required to react</p></li><li><p>For Boltzmann, same num molecules = area under graph same</p></li></ul><p></p>
8
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Effect of conc on reaction rate

  • If conc increase = increase num molecules

  • Also be more molecules with energies above activation energy

<ul><li><p>If conc increase = increase num molecules</p></li><li><p>Also be more molecules with energies above activation energy</p></li></ul><p></p>
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Catalyst

  • Increase rate by providing alternative reaction pathway with lower activation energy

  • Chemically unchanged by end of reaction

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Heterogenous catalyst

Catalyst different phase from reactants i.e. different physical state

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Homogeneous catalyst

Catalyst in same physical state as reactants

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Catalytic converters

2CO + 2NO —> 2CO2 + N2

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Rate of reaction

(amount reactants used/products formed) / time

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Dynamic equilibrium

  • Forward reaction = backward reaction

  • In closed system

15
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Le Chatelier’s Principles

  • Increase conc of reactants = increase products

  • Increase pressure = shift side fewer gas moles

  • Increase temp = shift endothermic side

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Alcohol production from alkene

  • 60-70 atm

  • 300 degrees Celsius

  • Phosphoric acid catalyst

  • High pressure = increase yield & rate

  • Exothermic so low temp favoured = increase yield but decrease rate

  • C2H4 (g) + H2O (g) ⇌ C2H5OH (g) ΔH = -46 KJmol-1

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Kc

  • Kc changes with temp

  • If Kc increases = quantity products increases & quantities reactants decreases = equilibrium shifts right

<ul><li><p>K<sub>c</sub> changes with temp</p></li><li><p>If K<sub>c</sub> increases = quantity products increases &amp; quantities reactants decreases = equilibrium shifts right</p></li></ul><p></p>