chemical energetics (H2)

Chemi lee SG

Dear ultimaonline,

i would like to ask if 1)doubling the volumes of acids &bases used in a neutralization reaction double the amount of heat released? Explain.

2) doubling the concentrations (but not the volumes) of acids &bases used in a neutralization reaction double the amount of heat released? Explain.

thanks.

Shootme SG

1) no 2) yes

Q=mcT

let X = no. of moles

H= standard enthalpy of neutralization

original XH=mcT

T= XH/mc

for 1) double vol. = double the no of moles = double the mass

2XH=2mcT

T=XH/mc (heat released is the same)

for 2) double conc. = double the no of moles only

2XH=mcT

T=2XH/mc ( double the amt of heat released)

UltimaOnline SG

Excellent working and answer by Shootme.

In absolute terms, both cases generate the same, double, amount of heat (compared to before the doubling). . However, in terms of observable temperature rise, only the latter case will register greater temperature change (compared to before the doubling).

Conceptually, this is due to the fact that when you double the volume of solution, the greater volume of water will absorb the greater amount of heat evolved, resulting in no further temperature change (compared to before the doubling). Mathematical working-wise, by Shootme has provided the proof.

Any further question, Chemi lee?