kylegg4

Natural selection includes sexual selection, atleast this is what i thought anyway. For example the idea that elephants evolution resulted in smaller tusks because the larger tusks elephants were hunted therefore only smaller tusks males remained leaving only smaller tusked males to pass on their genes resulting in more smaller tusks elephants.

On my walk home this afternoon I was wondering if humans will evolve dramatically or even further than we have already, not acknowleding the evolution knowledge and technological of course. I was just thinking on the premise of natural selection. Have our emotions evolved too much for our physiology to evolve or change any more dramatically away from its current state, what factors could affect this evolution? I'm not sure if this will make sense so please say if it doesn't.

if it is a completely closed system then enthalpy does not change?

Ok so i havnt actually got the whole exo and endo round the wrong way i've just got the wrong idea about bonds, if bonds are broken enthalpy decreases? if bonds are formed enthalpy increases? so enthalpy increases because heat is released when the electrons go into what you called "low energy states? but when these bonds are broken the enthalpy decreases because energy is used to break the bonds so energy is "used up" and can nolonger be measure as part of the enthalpy of the system?

"Endothermic reaction have positive enthalpies" is this one of those negative is positive and positive is negative. because you said earlier that endothermic reactions can be described as [math] \Delta H [/math]<0 which means a decrease in enthalpy? or am i just way off!?

"bond breaking is endothermic, bond forming is exothermic." if endothermic reactions are [math] \Delta H [/math] less than zero then does that mean energy of that system is decreasing so bonds contain energy you break bonds energy is lost(endo) you create bonds with energy (exo) then [math] \Delta H [/math] is larger than zero? Ok, so you ignore single properties of the whole system you're just talking about the system as a whole...much like entropy.

"These reactions talk about the result, not the process." Yes ok so say i do a reaction like A+BC--->AC+B then one product is losing energy and one is gaining, so what do i say the end result is? A gain more energy and B losing energy but C also gains???? Has this any relevance as to whether it's exothermic or endothermic?

I'm a little unsure on endothermic and exotermic reactions. an endothermic reaction absorbs heat (the product will become hot) and an exothermic reaction gives off heat (the product will become cold) But if i react two products together will exo and endo occur at the same time? Because, for example in a replacement reaction one product gains some more energy and the other loses energy.