and Chemistry? Joules or calories

Evidence of Energy  Motion  Heat  Light  Sound

Energy Units  joule ≡ energy exerted by a force of one Newton acting to move an object through a distance of one meter (SI unit)  calorie ≡ the amount of energy required to heat 1 gram of water 1 o C  Calorie = 1000 calories  1Joule = cal

How much is 1 Joule of energy?  the energy required to lift a small apple one meter straight up.  the energy released as heat by a quiet person, every hundredth of a second.  the kinetic energy of an adult human moving a distance of about 6 inches every second.

Types of Energy  Chemical  Heat  Light  Sound  Electrical  Magnetic  Motion  Nuclear Chemical Thermal Electromagnetic Kinetic Nuclear Acoustic Light Gravitational E E

Energy Transformations Chemical Thermal Electromagnetic Kinetic Nuclear Acoustic Light Gravitational E E

Energy Transformation

Either or Energy  Energy can be sorted into one of two categories – either either –kinetic (the “doing the work” phase) or or –potential (the getting ready to do work or the “stored” phase)

Energy examples Energy examples Potential Mechanical Energy and ? Potential Mechanical Energy and ? Kinetic Mechanical Energy and ? Kinetic Mechanical Energy and ?

Forms of Kinetic Energy Electrical – movement of electrons Electromagnetic – moving electro magnetic waves (light, x-rays, gamma rays, radio waves) Thermal – vibrations and movements of particles in a substance Mechanical – movement of objects Sound – movement of particles as energy travels through a medium Forms of Kinetic Energy Electrical – movement of electrons Electromagnetic – moving electro magnetic waves (light, x-rays, gamma rays, radio waves) Thermal – vibrations and movements of particles in a substance Mechanical – movement of objects Sound – movement of particles as energy travels through a medium

Potential Energy Chemical – energy stored in the bonds of molecules Stored mechanical – energy stored in an object based on its position relative to some reference state (i.e. a wound springs, a stretched rubber band, a boulder perched on the edge of a cliff) Nuclear – energy stored in nucleus of an atom Gravitational – energy stored based on relative position of two objects Potential Energy Chemical – energy stored in the bonds of molecules Stored mechanical – energy stored in an object based on its position relative to some reference state (i.e. a wound springs, a stretched rubber band, a boulder perched on the edge of a cliff) Nuclear – energy stored in nucleus of an atom Gravitational – energy stored based on relative position of two objects

How much energy is stored in glucose? C 6 H 12 O 6 1 gram of carbohydrate releases 4 Calories when burned 1 gram of fat releases 9 Calories when burned

Chemical Energy  Energy is stored in the bonds between atoms.  When chemical reactions occur, bonds are broken and formed.  The amount of energy released / absorbed during a chemical reaction can be measured and calculated from the bond energies

Bond Energy   Energy is absorbed by atoms when their bonds break. (+ΔH) ≡ heat of bond breaking   Energy is released when bonds form between atoms. (-ΔH) ≡ heat of bond formation

Bond Energy - Analogy Imagine stretching a rubber band until it breaks. You must do work to stretch the band because the tension in the band opposes your efforts. You lose energy; the band gains it. Something similar happens when bonds break in a chemical reaction. The energy required to break the bonds is absorbed from the surroundings.

Bond Energy Bond Energy (kJ/mol) H - H436 C - H413 N - H kJ is stored in H-H 436 kJ is released when H-H is broken The higher the bond energy, the more work is required to break the bond, the more stable it is

Bond Energy Bond Energy (kJ/mol) Bond Energy (kJ/mol) H - H436N - N160 C - H413N = O631 N - H393N triple N941 P - H297N - O201 C - C347N - P297 C - O358O - H464 C - N305O - S265 C - Cl397O - Cl269 C = C607O - O204 C = O805C - F552 O = O498C - S259

Bond Energy   Energy is absorbed when bonds break.   Energy is released when bonds form.   Energy is absorbed or released when the heat capacities of the products and reactants differ.

Calculating Energy of a Reaction H 2 + Cl 2  2HCl Breaking H bond = 436 kJ/mol Breaking Cl bond = 242 kJ/mol H-Cl bond forming = -431 kJ/mol

Reactions and Energy If heat is generated during a reaction ≡ exothermic If heat is absorbed during a reaction ≡ endothermic

Calculating Energy of a Reaction H 2 + Cl 2  2HCl Moles of Bonds Broken Energy absorbed (kJ) Moles of Bonds Formed Energy released (kJ) kJ kJ Heat of Reaction is 679 – 854 = -175kJ; energy is released during the reaction Endothermic or exothermic?

Chemical Reactions and Energy H 2 + Cl 2 Bonds are broken HCl Energy released

Calculating chemical energy N 2 + O 2  2NO Breaking one N bond = 946 kJ/mol Breaking one O bond = 498 kJ/mol Forming 2 N-O bonds = 2 x 631 kJ/mol = 1262 kJ/mol Net energy released = ( ) + 2(-631) = +182 kJ/mol Endothermic or exothermic?

Chemical Reactions and Energy N 2 + O 2 Bonds are broken NO Energy absorbed

Calculating chemical energy 2H 2 + O 2  2H 2 O Endothermic or exothermic?

Calculating chemical energy CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O (l) Endothermic or exothermic?

Food – the ultimate potential energy C 6 H 12 O 6 + O 2  CO 2 + H 2 O + energy ATP + heat

What is energy? Do I need energy? Where does energy come from?

Where does the energy in food come from? CO 2 + H 2 O + energy  C 6 H 12 O 6 + O 2 sun