calories • A calorie is the old chemistry metric unit for Nutrition and Calories energy. Nutrition and units • A calorie is the amount of energy required to • Calorie is an energy measurement just like raised 1 g of water 1 degree Celsius. joules. • In science, there was a broad unification • Calories reported on food labels are actually movement to make all sciences use the same kilocalories (it does have to be capitalized). units. • 1 Cal = 1000 cal = 4.183 kJ • A joule was the amount of energy commonly used in physics. • The calories in a food are the amount of energy released during the metabolism reaction of that • It is the amount of energy required to accelerate a 1 kg object 1 m/s2 for 1 m, or apply 1 N of food. force for 1 m.

Elsewhere Bomb Calorimeter Bomb Calorimeter

• Other countries • In the past food, was placed in a bomb are switching calorimeter, a sealed container to stop heat their food transfer, and burned to check the amount of labels to match energy released. the science • The heat was used to heat water and it could standard. be calculated. • This led to some problems as certain things we eat are indigestible, but they are burnable

Energy content in foods Better calculations Continued… • carbohydrate – 4 Cal/g • protein – 4 Cal/g • Now, the amount of proteins, • The energy from food is used by your body for • fat – 9 Cal/g carbohydrates, and fats are separated and everything it does (powering muscles, building measured. • There is more you need from food than just new cells, controlling body temperature etc.). energy (vitamins, minerals etc.). • We can calculate the caloric content from • If you take in less than you need your body • There is a certain amount of Calories you need to that and get a much better measure of the function. cannot function properly (car without gas). energy content of food. • This amount differs for each person, and differs • If you take in more than you use, it is stored as fat over time. or glycogen, organic compounds that can be • Striking an appropriate balance between these is a digested later. healthy diet.

1 Storage Enthalpy How is that different from q

• The ability of your body to store energy is • ~A measure of heat energy content of a • q is the change in heat energy. NOT bad. reaction. • Enthalpy is the change in heat energy per mole • You would have to eat every hour of your • The symbol for enthalpy is H for a process or reaction. life to survive if you couldn’t store energy. • Enthalpy can only be measured as a change • H = q/n • Excess long term storage of fat is not from a standard state. • so it is measured in J/mol healthy for your body. • Negative values mean the energy is released • 2 H + O → 2 H O H = -572 kJ/mol • Several methods of removing the excess fat (exothermic). 2 2 2  are not healthy either. • Positive value mean the energy is absorbed • This means if the reaction is run once with 2 (endothermic). moles of H2 and one mole of O2, 572 kJ of energy are released

Hess’s Law Hess’s Law example Another Hess’s Law example C + O  CO H = -394 kJ/mol • ~In going from a set of reactants to a set of graphite 2 2 • N2 + 2 O2 → 2 NO2 H = 68 kJ   products the change in enthalpy will be the Cdiamond + O2 CO2 H = -396 kJ/mol same regardless of how it changed. •Calculate H for the conversion of graphite • Or to diamond: • C (s)  C (s) • There is more than one way for a set of • N2 + O2 → 2 NO H = 180 kJ graphite diamond  reactants to produce a set of products. The • 2NO + O →2 NO H = -112 kJ H for the reverse of a reaction will be the 2 2 opposite sign. overall energy change will be the same no • 68 kJ matter how you get there.

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