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Understanding Energy and Chemical Bonding in Chemistry

Learn about the forms of energy - potential and kinetic, and how they relate to heat transfer and work in Chemistry. Understand chemical bonding including ionic and covalent bonds, along with thermochemical equations for reactions.

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Understanding Energy and Chemical Bonding in Chemistry

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  1. Energy potential kinetic • energy possessed by an object in virtue of its motion. • Ekin=1/2 mv2 • Ekin=3/2 RT Heat is the energy transferred from one object to another in virtue of T-difference Never confuse T and heat Energy: Ability to do work or produce heat. Work=force x distance force causes the object to move • Gravitational force causes the water to fall. • can generate electricity

  2. Potential energy: • energy possessed by an object due to its presence in a force field i.e. under the effect of external force. • Object attracted/repelled by external force. • stored energy! Attraction causes the ball to fall, h smaller, Epot smaller. Epot=mgh Attraction causes the potential energy to decrease. Repulsion causes the potential energy to increase.

  3. Compounds Ionicmolecular consist of ionssharing of electrons Ionic bondcovalent bond Chemical Bonding III/

  4. Covalent Bond sharing of electrons (non-metals +non-metals) H● + ●H→H● ●H H + H →H-H H H H H ● ● ● ● High probability of finding the electrons III/

  5. repulsion e- e- + + attraction attraction dominates repulsion dominates III/

  6. Ionic Compounds:Sodium chloride Lattice: Arrangement in a periodic manner giving ordered structure. • Lattice energy: • Energy released when separate ions (i.e. no interaction between them) gather forming a crystal: • )Na+(g) + Cl-(g) → NaCl(s • The lattice energy is the crucial factor responsible for the stability of ionic compounds. III/

  7. C=O C-H O=O O-H R Ep P Chemical Energy CH4(g) +2O2(g)→ CO2(g) + 2H2O(g) • Chemical reaction: • No change in the number/nature of atoms • Redistribution of Bonds (change in bonding) • Change in attraction & repulsion forces between the atoms • Change in the potential energy Ep of molecules • Energy is conserved! • Energy difference released as heat. • Heat of reaction (Qv, Qp). • Reaction exothermic. DHreaction= Hf – Hi = HP – HR < 0

  8. N=O N≡N O=O P Ep R N2(g) + O2(g)→ 2NO(g) • Energy is conserved! • Energy difference obtained from surroundings as heat. • Heat of reaction (Qv, Qp=DE, DH). • Reaction endothermic. DHreaction= Hf – Hi = HP – HR > 0 DEreaction= Ef – Ei = EP – ER > 0 • Ep(R) > Ep(P), reaction exothermic • Ep(R) < Ep(P), reaction endothermic

  9. Thermochemical equation moles CH4(g) +2O2(g)→ CO2(g) + 2H2O(g) DHo=-802.3 kJ 1 mole of gaseous methane (CH4) reacts with two moles of gaseous molecular oxygen producing 1 mole of gaseous carbon dioxide, 2 moles of water vapor and 802.3 kJ of heat. N2(g) + O2(g)→ 2NO(g) DHo=+180.5 kJ DHo: Standard heat of reaction: Standard conditions: T=25oC, p=1atm.

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