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| Pregunta | Respuesta |
| What is bond dissociation enthalpy? | The energy needed to break one mole of the bond to give separated atoms - everything being in the gaseous state |
| Compare the energy required to break bonds with the energy released when bonds are made during an exothermic reaction | Less energy is needed to break bonds than is released when bonds are made Released > needed |
| Compare the energy required to break bonds with the energy released when bonds are made during an endothermic reaction | More energy is needed to break bonds than is released when bonds are made Needed > released |
| Nitrogen reacts with hydrogen to form ammonia in the reaction: N₂ + 3H₂ --> 2NH₃ The energy needed to break all the bonds in N₂ and H = 2253kJmol⁻¹ The energy released when forming the bonds in NH₃ = 2346kJmol⁻¹ Is this reaction endothermic or exothermic? | The amount of energy released is bigger than the amount needed, so the reaction is exothermic (ΔH is negative) |
| What is the name for the difference between the energy absorbed and released? | Enthalpy change of reaction Enthalpy change of reaction = (total energy absorbed) - (total energy released) |
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Calculate the enthalpy change for the following reaction:
N₂ + 3H₂ --> 2NH₃
Image:
Image (binary/octet-stream)
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Bonds broken = 945 +3(436) =2253kJmol⁻¹ Bonds formed = 6(391) = 2346kJmol⁻¹ Enthalpy change of reaction = 2243 - 2346 = -93kJmol⁻¹ (exothermic) |
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