Chapter 5

Energy

화학반응에서 에너지의 역할

Energy

• Energy is the capacity of do work– work is a measure of energy

• 에너지는 생성 / 소멸되지 않는다– 열역학 제 일 법칙– 에너지 보존의 법칙

Work and Force• May the force be with you!

Energy for Gravity• Gravity

– force of attraction between bodies

– imparts energy to bodies

• Potential Energy (P.E. ; V)– position dependent; stored energy

• Kinetic Energy (K.E. ; T)– energy of movement

Energy for chemical system

• Potential Chemical Energy– electron moves away from nucleus– electron moves toward each other

• Kinetic Chemical Energy– electrons are in constant motion– atoms, molecules, solids are also in motion

Energy

• Chemical Reaction– require a change in energy to occur– reactions absorb or release energy

• Forms of Energy– Heat – Light (electromagnetic wave, EMW)– Motion

Heat

• Heat – motion of atoms and molecules– 일종의 운동 에너지– K.E. = (3/2)RT

• Temperature– measure of the average kinetic energy

• Celsius(oC) and Kelvin(K)– scales for the measurement of temperature

섭씨 , 절대온도 , 화씨

Light• Light

– visible form of electromagnetic wave (EMW) or radiation

• Electron absorb light to move from lower energy levels to higher energy levels

• Light can cause reactions

• Other form of electromagnetic radiation– microwaves– UV(ultra violet) radiation

Light

• Speed of light = 3.0 X 108 m/s

• wavelength – 400 - 750 nm

• frequency– 1015 Hz = 1000 THz

• frequency = speed of light/wavelength

Energy Transfer• Energy Content

– H = enthalpy at constant pressure H = enthalpy change

= H(final) - H(initial)

• Energy released– exothermic ( -H )

• Energy absorbed– endothermic ( +H )

Energy Unit

• Energy Unit = Joule (J)– 1 cal = 4.184J– 1 kcal = 1000 cal = 4184 J– 1 Cal = 1000 cal

• cal > J

• Calorimeter

Bond Energies• Reaction break and form bonds

– Table 5.2 “mean” bond energy

• Electrons and atoms are reorganized– change in energy is required

• Reaction = bond reorganization– Bond breaking - endothermic– Bond making - exothermic

Energy of Reaction

Fuel Research

– -98kJ/mol exothermic reaction– reaction product = gas

– www.abc.net.au/science/news/stories/s63460.htm

Why Do Reaction Happen?

• Matter has a tendency to disperse energy

• Entropy - – measure of disorder– disorder in matter & energy

• Tendency for Entropy constantly increases– 열역학 제 이 법칙– 계와 환경 전체의 엔트로피 고려

Spontaneous Reaction• Spontaneity -

– ability of a reaction to disperse matter and energy

• Spontaneous Reaction– reactant go to products without input of energy

• Non-spontaneous Reaction– reactants need constant energy to become

products

Entropy

2 H2O 2 H2 + O2 H = +286kJ/mol

• Entropy?– Matter dispersion ; Liquid gas + gas – Energy concentration ;

• Spontaneous?– NO but needs something else (battery)

Chemical Kinetics• 화학 반응 속도론• Activation Energy (Ea, 활성화 에너지 )

• Energy from Collisions– atoms, molecules, ions– kinetic energy

Chemical Kinetics• Chemical Kinetics

– study of the rates of reactions– macroscopic rate

• Factors that affect Rates– temperature = kinetic energy

• 10 도 상승에 속도 2 배 상승

– concentration (mol/L)• 요오드 시계 반응

Catalyst

• 촉매– 반응에 관여하여 반응속도를 증가시키나– 변하지 않고 회수되는 물질– 적은 양으로 충분

• 촉매의 원리– 활성화 에너지를 낮춘다– 반응 경로의 변화– 반응속도 10 억 배 이상 증가

Catalytic Converter• 12 장 참조

Pd & Ptcatalyst

Enzyme - bio catalyst

• 아미노산 사슬= 단백질 분자

• 기질 (substrate) 선택성• blocking the enzyme

Homework

• 교과서 190 쪽 5 장 연습문제– 2, 4, 5, 11 번– 마감 1/7 일 시험시작전

• 1/7 ( 월 ) 9 시 15 분부터 중간시험– 범위 서문부터 6 장 탄소에 의한 창조 까지– 계산기 준비

• 중간시험 후 수업 합니다 .

References• http://www.hhmi.org/news/burley.html

– Blocking the enzyme, aminoglycoside 3-N-acetyltransferase (right), could prevent bacteria from inactivating antibiotics, says HHMI investigator Stephen K. Burley.

• http://www.abc.net.au/science/news/print/print_63460.htm– H2O2 : rocket fuel for the 21C