Reaction temperature (delta)

[5614]

if you have an exothermic reaction then heat is given out.

 

so temperature increases... temp change is a positive value

 

yet delta(temperature) will give you a negative number because the change in temperature, final temp value is greater than the initial temp. value, so the temperature change = initial temp - final temp = negative number.

 

so we have:

positive change for temperature

negative delta(temperature)

 

why is the change in temperature (delta) is negative whilst there is a positive change?

[swansont]

"Change in" is usually defined as "final - initial"

[5614]

oh no, i've answered my own question with a bit of help from someone else...

 

basically in an exothermic reaction there's an increase of temperature externally...

 

however

ΔH or delta(temperature) will be a negative number because ΔH applies to the system... with in the system there is a temperature loss (the energy is transferred to the 'outside') so outside there's a temperature loss and within the system using ΔH we can see there's a heat energy loss.

[Silencer]

H is enthalpy, not temperature. That's very important to know.

[5614]

oh yeah, sorry...

 

h = u + pV

 

where:

u = internal energy

p = pressure

v = volume

 

ΔH = energy used in bond breaking reactions - energy released in bond making products.

 

oh one sec, now i am confused!

 

this paragraph:

"ΔH or delta(temperature) will be a negative number because ΔH applies to the system... with in the system there is a temperature loss (the energy is transferred to the 'outside') so outside there's a temperature loss and within the system using ΔH we can see there's a heat energy loss."

does it apply for ΔH or Δtemperature? or both?

[5614]

so if a liquid starts at 10 degrees and ends up at 20 degrees

 

is Δ(temperature) 10 degrees (from 20 - 10)... or... -10 degrees (from 10 - 20)?

 

i know this is true:

For an exothermic reaction, ΔH is negative... (from a trusted website)

but is H temperature, enthalpy or possibly both?

[ed84c]

why would H be temperature? enthalpy is energy required.

[5614]

entalpy is the sum of the internal energy plus the product of the pressure times the volume of the gas in a system

 

energy required.... if you mean energy required for a reaction to occur that's activation energy.

[ed84c]

i meant energy required for all bonds to break- enrgy made.

[Silencer]

You always do (final - initial). So in your example, 20 - 10 = 10 C change.

 

I'm lazy and don't know the latex and such that the forum uses, so you can deal with the un-pretty math.