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    Hi. The answer is -164. I know you need to multiply it by 2 because of the number of moles, but why is there a minus sign? How is this equation exothermic, aren't bonds being broken?

    Can someone explain to me?

    Thanks.
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    Plus is endothermic. Minus is exothermic.
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    (Original post by Collombia)
    Plus is endothermic. Minus is exothermic.
    Thanks for the reply. How is this an exothermic reaction? I don't understand. I'm not the best at chem....
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    (Original post by greentron6)
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    Hi. The answer is -164. I know you need to time it by 2 because of the number of moles, but why is there a minus sign? How is this equation exothermic, aren't bonds being broken?

    Can someone explain to me?

    Thanks.
    Okay so enthalpy of formation refers to the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions. In this case, the enthalpy of formation of N2O is positive, meaning it is endothermic.

    The reaction we're shown is the decomposition of N2O, i.e. the reversal of enthalpy of formation. Therefore, you reverse the sign as well, so you get -82kJmol-1. Now, since there are two moles of N2O, you multiply the value by 2 as you said, giving
    -164kJmol-1!

    Hope that makes sense
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    (Original post by greentron6)
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    Hi. The answer is -164. I know you need to time it by 2 because of the number of moles, but why is there a minus sign? How is this equation exothermic, aren't bonds being broken?

    Can someone explain to me?

    Thanks.
    In any reaction, bonds are both being broken AND made. Though, the energy values for breaking and making bonds are different most of the time. If a reaction is exothermic, it doesn't mean that no bonds are being broken, it means that it takes more energy to make the bonds than it did to break them.
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    Bonds are being broken but then stonger bonds are made (NΞN and O=O) so overall energy is released
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    (Original post by Don Pedro K.)
    Okay so enthalpy of formation refers to the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions. In this case, the enthalpy of formation of N2O is positive, meaning it is endothermic.

    The reaction we're shown is the decomposition of N2O, i.e. the reversal of enthalpy of formation. Therefore, you reverse the sign as well, so you get -82kJmol-1. Now, since there are two moles of N2O, you multiply the value by 2 as you said, giving
    -164kJmol-1!

    Hope that makes sense
    So in order to form N20, 82kJ mol-1 will be required?
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    The value given for enthalpy of formation is +ve

    Since the equation given is the opposite of enthalpy of formation as its
    Substance -> constituents rather than
    Constituents -> Substance which is enthalpy of formation

    then the enthalpy change is the opposite, therefore -ve.
    Enthalpy formation can be either +ve or -ve as mentioned by posters above.
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    (Original post by greentron6)
    So in order to form N20, +82kJ mol-1 will be required?
    Yeah in order to form 1 mole of N2O under standard conditions.
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    (Original post by Don Pedro K.)
    Yeah in order to form 1 mole of N2O under standard conditions.
    Thanks!
 
 
 
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