Enthalpy change question help !!

Hi, I would like to know the effect of increasing the volume of water in both enthalpy change of neutralisation and enthalpy change of solution.

For enthalpy change of neutralisation, even if you increase the volume of solution, the answer is that ' temperature change is the same as twice the energy is released but it is spread over twice the volume of solution.

Whereas with enthalpy change of solution, increasing the volume of water will cause the temperature change to decrease as same energy/heat spread over larger volume of water

I don't really understand the difference between the two.

Thanks

Reply 1

username1869653

18

Original post by coconut64

Hi, I would like to know the effect of increasing the volume of water in both enthalpy change of neutralisation and enthalpy change of solution.

For enthalpy change of neutralisation, even if you increase the volume of solution, the answer is that ' temperature change is the same as twice the energy is released but it is spread over twice the volume of solution.

Whereas with enthalpy change of solution, increasing the volume of water will cause the temperature change to decrease as same energy/heat spread over larger volume of water

I don't really understand the difference between the two.

Thanks

If you increase volume of solution, you are also increasing the amount of reactant you have. If you increase the volume of water alone, however, you are simply diluting the solution. Hope I helped.

Reply 2

coconut64

OP

16

Original post by ugaaa5

If you increase volume of solution, you are also increasing the amount of reactant you have. If you increase the volume of water alone, however, you are simply diluting the solution. Hope I helped.

I just don't get the bit about the temperature change instead of the concentration of reactants. Thanks

Reply 3

username1869653

18

Original post by coconut64

I just don't get the bit about the temperature change instead of the concentration of reactants. Thanks

That's what I was trying to illustrate. One second, let me think of a way to illustrate this otherwise.

Reply 4

username1869653

18

Original post by coconut64

I just don't get the bit about the temperature change instead of the concentration of reactants. Thanks

Temperature change comes from the reactants, not the solution itself. If you double the volume of solution, you are not changing how concentrated the solution is. You simply have double the amount of reactant, in double the amount of water, causing double the energy released. That energy is distributed as evenly as it was before.
If you add water, however, you are reducing the concentration of the solution overall. That means you have the same amount of reactant in more water. Although the energy released is the same, the temperature change decreases as the energy released from the reaction is distributed over more water.

Reply 5

coconut64

OP

16

Original post by ugaaa5

Temperature change comes from the reactants, not the solution itself. If you double the volume of solution, you are not changing how concentrated the solution is. You simply have double the amount of reactant, in double the amount of water, causing double the energy released. That energy is distributed as evenly as it was before.
If you add water, however, you are reducing the concentration of the solution overall. That means you have the same amount of reactant in more water. Although the energy released is the same, the temperature change decreases as the energy released from the reaction is distributed over more water.