What Is Energy?

1. What Is Energy? A comprehensive explanation…

2. 2.12 Water’s hydrogen bonds moderate temperature • It takes a lot of energy to disrupt hydrogen bonds • Therefore water is able to absorb a great deal of heat energy without a large increase in temperature • It has a very high specific heat (1 cal/g-K) • As water cools, a slight drop in temperature releases a large amount of heat

3. Heat, Temperature, & Evaporation • HEAT = amount of energy associated with the movement of atoms/molecules • Heat is the total amount of kinetic energy due to molecular motion in a body of matter. Heat is energy in its most random form • TEMPERATURE = intensity of heat (i.e., average speed of molecules rather than the total amount of heat energy) • A swimmer in the ocean: ocean is at a lower temperature than the human but the ocean has a lot more heat than the human • A water molecule takes a large amount of energy with it when it evaporates • This leads to evaporative cooling • Evaporation is comparable to having the fastest runner leave a team and thus lower the average speed of the team • Affected by humidity of air (amount of water in air)

4. 5.1 Energy is the capacity to perform work • Energy is defined as the capacity to do work • A somewhat circular definition of work is used also • All organisms require energy to stay alive • Energy makes change possible • Energy is the capacity to rearrange matter • Moving objects can do work by TRANSFERRING MOTION to other matter • E.g., pushing a cart up a hill

5. Two main categories…(but many forms!) • Kinetic energy is energy that is actually doing work • Associated with movement of molecules and atoms in a body • Also, light is a form of KE • Potential energy is stored energy (ability to do work) as a result of its LOCATION or STRUCTURE • Negatively charged electrons of an atom have PE owing to their positions in electron shells at a certain distance from the positive nucleus (farther it is, the more PE it has) • Chemical Energy is the PE of molecules and can be released to power the work of the cell (these are all manipulations of electromagnetic forces and the Electric Field) • Organic molecules have PE as a result of the arrangement of their atoms and bonds; this PE is the energy that is available to do the work of the cell

6. 5.2 Two laws govern energy conversion • First law of thermodynamics • Conservation of energy: DU = dQ + dW • Energy can be changed from one form to another • However, energy cannot be created or destroyed • Not so true at the quantum level…

7. Second law of thermodynamics • Energy changes are not 100% efficient • Energy conversions increase disorder, or entropy • Entropy is more properly related to the energy distribution of energy states of a collection of molecules, and this aspect is usually discussed in statistical mechanics.(http://www.science.uwaterloo.ca/~cchieh/cact/applychem/entropy.html) • Some energy is always lost as heat • This energy becomes unusable (unavailable to do work)

8. 5.3 Chemical reactions either store or release energy • Cells carry out thousands of chemical reactions per second • The sum of these reactions constitutes cellular metabolism • A cell is a chemical factory that transforms energy from one form to another

9. Products Amount of energy INPUT Potential energy of molecules Reactants There are two types of chemical reactions: • Endergonic reactions absorb energy and yield products rich in potential energy • Energy is stored in the covalent bonds of the product molecules

10. Reactants Amount of energy OUTPUT Potential energy of molecules Products Exergonic… • Exergonic reactions release energy and yield products that contain less potential energy than their reactants • Reactants’ covalent bonds contain more energy than those in the products • E.g., burning of wood releases the PE of glucose (which constitutes the carbohydrate, cellulose) as heat and light (and the products CO2 and H2O)

11. 5.4 ATP shuttles chemical energy within the cell • In cellular respiration, some energy is stored in ATP molecules • ATP powers nearly all forms of cellular work • ATP molecules are the key to energy coupling

12. Adenine Phosphategroups Hydrolysis Energy Ribose Adenosine triphosphate Adenosine diphosphate(ADP) Hydrolysis cleaves a high-energy phosphate bond! • When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction supplies energy for cellular work • All three phosphate groups are negatively charged • These like charges are crowded together • This mutual repulsion contributes to the PE stored in ATP (much like a compressed spring)

13. Pi is like a ball on a spring… • The phosphate bonds of an ATP are like coiled springs, barely held together by strings • When the string breaks, the spring uncoils and releases all the energy it had stored • The released energy pushes the ball towoards a wall, causing it to stick to the wall • This is equivalent to the Pi being attached to a target protein when the phosphate bond is broken/unravelled

14. Reactants Products Potential energy of molecules Work Protein ATP powers cellular work by phosphorylation… • How ATP powers cellular work • The transfer of a phosphate group to a molecule is called phosphorylation. • Most cellular work depends on ATP energizing other molecules by phosphorylating them Phosphorylation: Endergonic ATP -> ADP: Exergonic

15. How does ATP transfer energy from exergonic to endergonic processes in the cell? • By phosphorylation: the addition of phosphate groups. • Energy released in exergonic processes (like glucose breakdown during cellular respiration) is used to phosphorylate ADP to form ATP • This is an endergonic (energy-storing) reaction • ATP transfers energy to endergonic processes by phosphorylating other molecules • Working cell may consume and regenerate 10 million ATP molecules/second!!!

16. The ATP Cycle… • The ATP cycle Hydrolysis Dehydration synthesis Energy from exergonic reactions Energy for endergonic reactions Figure 5.4C

17. HOW ENZYMES WORK 5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers • For a chemical reaction to begin, reactants must absorb some energy • This energy is called the energy of activation (EA) or activation energy • This represents the energy barrier that prevents molecules from breaking down spontaneously • So how can specific reactions required by a cell get over the energy barrier? • One way might be to add heat • But this would speed up ALL reactions and too much heat would even denature proteins and so kill the cell

18. EAwithout enzyme EA barrier Enzyme EAwith enzyme Reactants Net change in energy Reactants Products 1 Products 2 Solution: Catalyst… • A protein molecule that functions as a biological catalyst is called an enzyme & can decrease the energy barrier • Increases rate of reaction without itself being transformed

19. Recap… • ATP breaks down easily and could spontaneously decompose if not blocked by an “energy barrier” • The energy barrier is the amount of energy that reactants must absorb to start a chemical reaction • The amount of energy required is called the Energy of Activation/Activation Energy (EA) • In ATP, EA is the amount of energy required to break the bond between the second and third phosphate group • Enzymes can lower activation energy by holding reactant molecules in specific positions.

20. 5.6 A specific enzyme catalyzes each cellular reaction • Enzymes are selective • This selectivity determines which chemical reactions occur in a cell • An enzyme protein has a unique 3-d shape which determines which chemical reactions it catalyzes • A single enzyme molecule may act on thousands (or even millions) of substrate molecules per second!

21. Activesite Enzyme(sucrase) Substrate(sucrose) How enzymes work… Glucose Fructose 1 4 Enzyme available with empty active site • The enzyme is unchanged and can repeat the process Products are released 3 2 Substrate is converted to products Substrate binds to enzyme with induced fit Hydrolysis of sucrase substrate

22. 5.7 The cellular environment affects enzyme activity • Enzyme activity (which depends on its shape & structure) is influenced by • temperature • affects molecular motion • enzyme’s optimal temperature produces highest rate of contact between reactant molecules and the enzymes active site • higher temperatures denature enzyme, changing its 3-d shape • salt concentration • salt ions interfere with some of the chemical bonds that maintain protein structure • pH • Extra hydrogen ions (at low pH) also interfere with some of the chemical bonds that maintain protein structure • Some enzymes require nonprotein co-factors • Some cofactors are organic molecules called co-enzymes

23. General Conservation Laws – Blocks Analogy • You start your study of physics by first studying kinematics, the study of motion, which leads to • → Dynamics, the study of the causes of motion (i.e., Forces), which finally leads to • → Energy (or Energetics) • The basis for EVERY process/transaction (how forces are "paid" for) • Underlies all physical phenomena and, in fact, existence itself... • But this idea of energy is strange and elusive...

24. Energy is an abstract, mathematical idea • But, just like Copernicus' heliocentric "universe" & the idea of fields, it just happens to be real! • It's a numerical quantity which doesn't change • It is NOT a description or a mechanism • We have no idea of what energy is... • It's just a strange fact of nature: • Calculate some number • Watch nature go through her tricks • Calculate number again: same! • Just like in chess, the bishop always ends up on a red square after any number of moves

25. Leads us to… • Law of conservation of energy • A certain quantity (energy) does not change

26. Since abstract, illustrate by analogy (thanks to Prof. Feynman) • Suppose a child has 28 blocks (they’re indestructible, indivisible, identical) • Mother counts the # of blocks → she discovers conservation of blocks • Number of blocks always constant (i.e., doesn't change) • [# of blocks]before = [# of blocks]after

27. One fine day… • Some blocks disappear in a 16 oz. Box… BUT she can't look inside the box • If you didn't know the weight of each block, you could use the conservation law to figure out exactly how many blocks were hidden in the box: • [# of blocks]before = [# of blocks]after • constant = constant • 28 = 28 • 28 = (# of visible blocks) + (# of hidden blocks) •  (# of hidden blocks) = 28 - (# of visible blocks)

28. Suppose each block weighed 3oz • If she knew, or confirmed, that each block weighed 3 oz: • CONSTANT = 28 = (# of visible blocks) + (# of blocks hidden in box) 28 = (# of visible blocks) + ( [ (wt. of box) - 16oz ]/3oz ) • Now, suppose some blocks disappear in the dirty bathtub (originally 6 inches of water); each block raises water 0.25 inches, so: • CONSTANT = 28 = (# of visible blocks) + (# of blocks hidden in box) + (# of blocks hidden in bathtub) 28 = (# of visible blocks) + ( [ (wt. of box) - 16oz ]/3oz ) + ( [(height of water) - 6 inches]/0.25 inches ) • Increasing complexity of her world increases the number of terms representing ways of calculating # of blocks • Complex formula, quantity which has to be computed and always stays the same: • 28 = (# of visible blocks) + (# of blocks hidden in box) + (# of blocks hidden in bathtub) + ...

29. No visible blocks! • Eventually, actual number of visible blocks goes to zero! • The mother has to infer the existence of the number of blocks • And, she can use the process in reverse... if she knows she should end up with 28 blocks, she can infer how many blocks should be in the box or tub • This is what makes conservation laws so useful... if you know what the number should be (either before or after), you can find intermediate values

30. Energy also hidden! • Like block example, many different forms in which energy hides (with a formula for each one): • Two categories of energy: potential and kinetic • Many different forms of energy within each category: • Some forms of energy are: gravitational, heat, elastic, electrical, chemical, radiant, nuclear, and mass energy • But TOTAL energy obeys strict conservation law • Just like in Fnet =manet there were many different kinds of forces that went into determining Fnet (you had to add up all the different kinds of forces, using their individual formulae, to get Fnet), in the same manner, there are many different kinds of energy that you need to consider the formulae for in order to figure out conservation of TOTAL energy. • I.e., [#]before = [#]after

31. Work is key to energy • Energy takes many forms (e.g., gravitational, elastic, etc.) but falls into only two categories (potential and kinetic) • A good metaphor for energy is financial assets/net worth, which comes in many forms: cash, investments, real estate, etc. but only two categories: liquid (spendable) and invested (can’t immediately buy stuff with it) • Every interaction in our universe involves the transfer or transformation of energy • "That which is transferred when work is done" (p. 94) is very much like ancient Indo-European mystics • An exact definition of energy is elusive (just like an exact definition of any of the fundamental quantities was impossible)… so we do what we did before: • We define it relative to some other quantity (in this case, a strange fact of nature we call Work)

32. Look at lever… = 100N w = 300N • We happen to find when we calculate (like blocks analogy): • Fleft/Fright = dright/dleft • F • d has same value on both sides  Work • Task requires same energy whether we: • move smaller dist with larger F • move longer dist with smaller F • Work = F · d (d is in the direction of the vector F) regardless • Units of Work: 1 J = 1 N-m  A measure of how much energy is transferred or transformed

33. 30kg barrel raised 1.2m; amount of work done? W = F * d = m * a * d = 30kg * 9.8m/s2 * 1.2m = J In Class Exercise #2: W = ?J m = 30kg Δd = 1.2m agravity = g = 9.8m/s2

34. Examples of Work • No mechanical work done in carrying box • When lifted, work is done against gravity • When dropped, by gravity • Comes in pairs: work is done by one force and against the other force in the pair • Example of catching ball • Move hand back when catching = smaller Force • Work is still the same! (The ball has a certain KE which it has to dissipate in order to stop, v=0) • Ball does work on hand • More distance == more Work OR more Force == more Work

35. 2nd Conservation Law: Energy • Energy is the measure of a system's capacity to do work • Energy is transferred (or transformed) when work is done • Units of energy = units of work (Joules) • In mechanics, two main forms of (mechanical) energy: • Work done on a system results in Kinetic Energy whereas the ability to have work done by a system is called its Potential Energy • Work always results in transfer of energy, transformation of energy, or both • Work done on a system increases its Energy • Work done by a system decreases Energy • Work done within system  Energy transformation

36. KE & PE • KE = energy due to motion (can be converted to Work) • Depends only on final speed • (mechanical) KE = ½ mv2 (double v = quadruple KE) • Derivation on p. 95 • W = Fd = (ma) (½ at2) = ½ m (at)2 = ½ mv2 • KE is relative since v is relative (ship example) • PE = energy due to position • Equal to work done on it to get it to that position (STORED work, or the ability to do work) • Work done in lifting it is stored as gravitational PE • Different kinds of PE: • Gravitational PE • Elastic PE • Depends on how strong spring is & how much stretched or compressed • Internal PE (whenever you see Internal Energy == Think Heat) • Just KE and PE of atoms (heat) • (Mechanical) Energy cannot be created or destroyed • Total energybefore = Total energyafterE = KE + PE = CONSTANT

37. If I drop something from 10 m, how fast will it be going at the bottom? PE = KE mgh = ½ mv2 v doesn't depend on mass! In Class Exercise #3: v = ?m/s di = 10m df = 0m agravity = g = 9.8m/s2

38. Collisions & Power • Elastic collision: KEbefore = KEafter • Inelastic collision: KEbefore ≠ KEafter • Irrespective, total linear momentum is always conserved • In an inelastic collision, like car crash: • Some energy goes to Internal Energy (heat), sound, etc. • Whenever you see internal energy, think heat • Power = rate of doing work or transferring energy • P = Work/t = Energy/t • Units of Power: Watts • 1 W = 1 J/s • Power and speed are both rates of change

39. Temperature • Intimately tied to the idea of Energy (see intro to analogy for energy) • Three scales: • Fahrenheit, Celsius, and Kelvin • Kelvin Temperature is a measure of the average KE of particles → particles have KE! • Higher temperature → particles move faster → higher KE • http://plabpc.csustan.edu/general/tutorials/temperature/temperature.htm • Liquids/Solids are bound (solids bound more tightly than liquids; • Imagine connected with springs) → some particles also have PE! • Vibrate through greater distance when Temperature goes up • This vibrational/elastic PE is important in phase changes • PE is negative when bound • http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html#c3

40. Temperature vs. Internal Energy • (Kelvin) Temperature is a property of a typical molecule of a substance -- how many molecules there are doesn't matter • Internal Energy, on the other hand, is the total energy of all the particles • E.g., you can have a few high speed particles in a very dilute gas, giving it a high temperature but little total energy, or many low speed particles in a dense liquid, giving it a low temperature but a greater total energy overall. The high temperature dilute gas would not be able to transfer much heat to a cooler substance but the lower temperature liquid would! • Absolute Zero (-273.15 oC) • Average KE almost zero • Cannot be reached: HUP • Low temperatures: superfluids, superconductors, etc. • High temperatures: KE high so no binding so no liquids/solids • Above 20,000 K electrons break free: plasmas only

41. Two ways to increase Temp (or energy, since T = KE) • 0th Law of Thermodynamics: • Temp measures thermal equilibrium (Ta = Tb = Tc so Ta = Tc) and heat flows from THto TL • Expose to reservoir at higher Temp (HEAT TRANSFER) • Doing Work on it (WORK TRANSFER) • Experiment by James P. Joule established established relationship between mechanical work and heat • Temperature depends on average KE of atoms and molecules • 1st Law of Thermodynamics • Internal Energy (of atoms & molecules): U = (KE + PE)atomic • Gases only have KE • Liquids/solids also have PE (since they're bound and oscillate)

42. U increases with increasing Temp • Heat, Q, is a form of energy that flows from TH to TL • As Heat flows, energy is transferred (like work in mechanics) • As work is done, energy is transferred/transformed in mechanics • Q and W are energy in transition while U and PE are stored energy: • What quantities are measured in units of Joules? • Energy (KE, PE, and U), which is changed by: • Work • Heat • That's because they're all different forms of energy (stored or in transition)

43. Review the story so far... • Atoms have KE and PE → Internal Energy, U • We know Work (W) can change the energy (U) and is energy in transition • We also know that Heat (Q) changes Temperature (T) → which is equal to the average KE of the particles • Therefore, Q also changes energy and is also energy in transition • So if we can somehow find both Q & W, we can figure out exactly how much the energy of a system changes and don't need to know anything about the microscopic U of each atom!

44. 1st Law: CHANGE in Internal Energy • CHANGE in Internal Energy = ΔU = W + Q • http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html#c3 • W means work done on gas (+W = -pdV = -pΔV) and +Q means heat flowing into gas • W = F • d; but if something is dropped from a building, the distance is just the Δh; So W = F•Δh. But p = F/A so F = pA. Now Work becomes W = pA•Δh. But A•h is Volume so W = pΔV. Now, since Volume is decreasing (e.g., dropped from a higher height to a lower height), this is actually negative of that: +W = -pΔV • Restatement of conservation of energy • Internal Energy is essential to understanding phase transitions: • When Heat is transferred but Temp. remains same → Heat goes to PE (to break bonds) • We already know how to calculate work; so if we can now quantify heat, we can figure out ΔU without knowing anything about the microscopic nature of U!!!

45. Heat Transfer: Conduction(Solids & Liquids) • Conduction: transfer of energy via direct contact • Takes place at boundary between 2 substances • Via collision of atoms and molecules • Conduction poor in gases (direct contact rare) • Materials with trapped air become good thermal insulators • A rug is not warmer than cold floor • Poorer conductor → less heat conducted away from feet • Metals are good thermal conductors • Conduction electrons carry U from hot to cold areas (valence electrons available for bonding)

46. Heat Transfer: Convection(Fluids: Liquids & Gases) • Convection: transfer of energy by buoyant mixing in a fluid • Thermal Buoyancy: when fluid is heated, it's Density decreases • Hotter, less dense fluid rises • Cooler, denser surrounding fluid pushes it up → FB, just like in the Law of Archimedes we studied in the last chapter • Conduction occurs between warm, rising fluid and cold, static fluid • Cools and falls back down: mixing leads to convection currents • Examples: • Convection happens in the atmosphere & oceans: • Sun warming Earth leads to sea/land breezes and thermals • Sun warms water at Equator; leads to underwater currents

47. Heat Transfer: Radiation(EM Waves) • Radiation: transfer of energy via electromagnetic waves • Can operate in a vacuum • Emission is mainly in the IR part of the spectrum (for substances with T < 430oC) • U of atoms converted to EM energy: radiation • Radiation carries the energy through space until it's absorbed • Upon absorption, converted to U of atoms of absorbing substance • Everything emits EM Radiation • Hotter things emit more IR and Visible light • Emission of radiation cools; absorptionwarms • Cooling by emission is similar to cooling by evaporation (which is analogous to a baseball team's batting average going down when its best hitters are traded) • Hold hand to side of lightbulb: radiation warms • Place above, both radiation and convection of heated air warms

48. Summary • Atoms have both KE & PE → Internal Energy (U) • We know Work (W) is energy in transition and can change U • Since Heat (Q) changes the Temperature (T → is equal to the average KE of the constituent particles), we know that Q is alsoenergy in transition • So if we can find both Q & W, we can get the change in Internal Energy (ΔU) without any reference whatsoever to the microscopic U of each individual atom/molecule • Since we already know how to calculate (or quantify) Work, all we need to do is figure out how to quantify Heat (Q) now...

49. Specific Heat Capacity: Q = m c ΔT • Heat is transfer of energy • Units of Joules and c has units of J/kg-oC • Amount of Q needed to raise T of 1 kg by 1 oC • Larger c  more Q needed to raise T by 1oC • cwater is really high: can absorb or release large amounts of Q (that's why it's used in radiators, power plants, etc.)

50. How much heat must be added to 1 cup (0.3 kg) of water to boil it (raise it from 20 oC to 100 oC)? Note: cwater = 4.18 kJ/kg-oC (see example 5.2 on p. 186) Q = mc ΔT = 0.3kg * 4.18kJ/kg-oC * 80oC In Class Exercise #2: m = 0.3kg Q = ? J Ti = 20oC Tf = 100oC cwater = 4.18 kJ/kg-oC