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What is Energy

What is Energy
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RyanCanon,United Arab Emirates,Teacher
Published Date:21-07-2017
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Lecture 11 thermodynamics We’ll be dealing with the energy of chemical reactions How do you keep track of it? Where does it come from? Thermochemistry Energy   • Can  come  from  a  variety  of  sources:   Ø Light  (photochemistry)   Ø Electricity  (electrochemistry)   Ø Heat  (thermochemistry)   Thermochemistry What  is  Energy?   •  The  ability  to:   •   do  work     •  transfer  heat.   Ø Work:  Energy  used  to  cause  an  object  that  has  mass  to   move.   Ø Heat:  Energy  used  to  cause  the  temperature  of  an   object  to  rise.   Thermochemistry Work •  Energy  used  to  move  an  object   over  some  distance.   •  w  =  F  ž d,    w  =  work,     F  =  force     d  =  distance  over  which  the  force   is  exerted.     Note  units:   2 F  =  ma,  mass(distance/s )   2 2 W  =  F(d)  =  mass(distance /s )   Thermochemistry 2 =  mv  Heat   •  Energy  can  also  be   transferred  as  heat.   •  Heat  flows  from   warmer  objects  to   cooler  objects.   Thermochemistry Kinetic Energy  Energy  an  object  possesses  by  virtue  of  its   moMon.   1 2 KE = ⎯ mv 2 Thermochemistry PotenMal  Energy    Energy  an  object  possesses  by  virtue  of  its   posiMon  or  chemical  composiMon.   More potential E Less P.E. as bike goes down. Thermochemistry Transferal  of  Energy   a)  Add  P.E.  to  a  ball  by  liPing  it  to  the  top  of   the  wall   Thermochemistry Transferal  of  Energy   a)  Add  P.E.  to  a  ball  by  liPing  it  to  the  top  of   the  wall   b)  As  the  ball  falls,     2 P.E  -­‐-­‐-­‐-­‐-­‐-­‐  K.  E.  (1/2mv )   Thermochemistry Transferal  of  Energy   a)  Add  P.E.  to  a  ball  by  liPing  it  to  the  top  of   the  wall   b)  As  the  ball  falls,     2 P.E  -­‐-­‐-­‐-­‐-­‐-­‐  K.  E.  (1/2mv )   Ball  hits  ground,  K.E.  =0,  but  E  has  to  go   somewhere.  So   1.  Ball  gets  squashed   2.  Heat  comes  out.   Thermochemistry Energy accounting • We  must  idenMfy  where  different  types  of   energy  go.   • Therefore,  we  must  idenMfy  the  places.   Thermochemistry System and Surroundings •  The  system  includes  the   molecules  we  want  to   study  (here,  the   hydrogen  and  oxygen   molecules).   •  The  surroundings  are   everything  else  (here,   the  cylinder  and  piston).   Thermochemistry First Law of Thermodynamics •  Energy  is  conserved.   •  In  other  words,  the  total  energy  of  the  universe  is  a   constant;                    ΔE  =  -­‐ΛE   System surroundings Thermochemistry Internal Energy  The  internal  energy  of  a  system  is  the  sum  of  all   kineMc  and  potenMal  energies  of  all  components  of   the  system;  we  call  it  E.     E = E + E + E + E +…… internal,total KE PE electrons nuclei Almost impossible to calculate total internal energy Instead we always look at the change in energy (ΔE). Thermochemistry Internal  Energy    By  definiMon,  the  change  in  internal  energy,Δ   E,  is  the   final  energy  of  the  system  minus  the  iniMal  energy  of   the  system:        ΔE  =  E  −  E   final iniMal Thermochemistry Changes  in  Internal  Energy   • If  ΔE    0,  E    E     final iniMal Ø Therefore,  the  system   absorbed  energy  from   the  surroundings.   Thermochemistry Changes  in  Internal  Energy   • If  ΔE    0,  E    E     final iniMal Ø Therefore,  the  system   released  energy  to  the   surroundings.   Thermochemistry Changes in Internal Energy •  When  energy  is   exchanged  between   the  system  and  the   surroundings,  it  is   exchanged  as  either   heat  (q)  or  work  (w).   • That  is,  ΔE  =  q  +  w.   Thermochemistry ΔE,  q,  w,  and  Their  Signs   -q +q Surroundings hot plate adds suck heat out of heat to water Thermochemistry water. Sign  of  work   block pushes truck down does work on truck w - block w + Truck pushes block up. truck Does work on block w - truck w + block Thermochemistry