Hybrid and Electric Automobiles

                                                                                                             

                                                                                                           

                                                                    The fuel cell shown The fuel cell shown here is based on the here is based on the

combination reaction:combination reaction:HH22 + O + O22 H H22OO

DefinitionsDefinitionsThermodynamics Thermodynamics The study of energy and

it’s transformations.

Thermochemistry Thermochemistry The thermodynamics of chemical reactions.

Energy Energy The capacity to do work or transfer heat.

Work Work The energy required to move an object against an opposing force.

W = F dHeat Heat Derived from the movements of atoms and

molecules (including vibrations and rotations).

Types of EnergyTypes of EnergyKinetic Energy Kinetic Energy The energy of motion, energy in

action.

Ek = (1/2)mv2

Potential Energy Potential Energy The energy of position, stored energy.

Work & Chemical Reactions Work & Chemical Reactions For the vast majority of chemical reactions there are two types of work that can happen.– Mechanical Work – done by creating/destroying

a gas (i.e. automobile cylinder, air bag, etc.)– Electrical Work – A redox reaction flowing

through an external circuit (i.e. battery, fuel cell)

11stst Law of Thermodynamics Law of Thermodynamics

Energy is neither Energy is neither created nor created nor destroyed destroyed

(conservation of (conservation of energy)energy)

Internal Energy = heat + Internal Energy = heat + workwork

E = q + wE = q + w

EnthalpyEnthalpy

Enthalpy (H)Enthalpy (H) The change in The change in enthalpy, enthalpy, H, is defined as the heat H, is defined as the heat gained or lost by the system under gained or lost by the system under

constant pressure.constant pressure.

H = qH = qpp

Where qWhere qpp = the heat flow at constant = the heat flow at constant pressurepressure

Properties of EnthalpyProperties of Enthalpy

1.1. Enthalpy is a state function.Enthalpy is a state function.

2.2. Enthalpy is an extensive property.Enthalpy is an extensive property.

3.3. Enthalpy is reversible. If we reverse Enthalpy is reversible. If we reverse the reaction the magnitude of the reaction the magnitude of H H remains the same but the sign remains the same but the sign changes.changes.

4.4. The enthalpy change depends upon The enthalpy change depends upon the states of the reactants and the states of the reactants and products.products.

Commonly used for studying reactions,

especially combustion reactions.

Because pressure isn’t constant, the bomb calorimeter

measures E rather than H

Constant-Volume (Bomb) Constant-Volume (Bomb) CalorimetryCalorimetry

We’ll use this kind of calorimeter in lab

1. Calibrate the calorimeter in order to determine its specific heat.

2. The calorimeter minimizes heat transfer into or out of the system.

3. By measuring the change in the temperature of the solution, we can calculate the heat given off in a reaction.

Constant-Pressure CalorimetryConstant-Pressure Calorimetry

Energy Stored in Carbs/SugarEnergy Stored in Carbs/Sugar

The body breaks carbohydrates down into glucose The body breaks carbohydrates down into glucose (blood sugar), C(blood sugar), C66HH1212OO66, which is then combusted in , which is then combusted in our bodiesour bodies

CC66HH1212OO66 (s) + 6O (s) + 6O22(g) (g) 6CO 6CO22(g) + 6H(g) + 6H22O(l) O(l) HH° = -° = -2803 kJ2803 kJ

In terms of energy released per gram of glucose one In terms of energy released per gram of glucose one mole of glucose has a mass of 180 g so that mole of glucose has a mass of 180 g so that

-2803 kJ/(180 g/mol) = -2803 kJ/(180 g/mol) = 16 kJ/g16 kJ/g

Fuel values for foods are typically reported in Fuel values for foods are typically reported in Calories, which is stands for Kilocalories or kcalCalories, which is stands for Kilocalories or kcal

1 Cal = 1000 cal1 Cal = 1000 cal 1 cal = 4.184 J1 cal = 4.184 J 1 kcal = 4.184 kJ1 kcal = 4.184 kJ

So for glucose 16 kJ/g x (1 kcal/4.18 kJ) = So for glucose 16 kJ/g x (1 kcal/4.18 kJ) = 3.7 kcal/g3.7 kcal/g

Energy Stored in FatsEnergy Stored in Fats

If we take a typical fat, such as tristearin, CIf we take a typical fat, such as tristearin, C5757HH110110OO66 the reaction with oxygen in our cells is:the reaction with oxygen in our cells is:

2C2C5757HH110110OO66 (s) + 163 O (s) + 163 O22(g) (g) 114CO 114CO22(g) + 110H(g) + 110H22O(l) O(l) HH° = -° = -75,520 kJ75,520 kJ

In terms of energy released per gram one mole of In terms of energy released per gram one mole of tristearin has a mass of 891 g so that tristearin has a mass of 891 g so that

-75,520 kJ/(2-75,520 kJ/(2891 g/mol) = 891 g/mol) = 42 kJ/g42 kJ/g

In terms of kcal (Calories) tristearin would be In terms of kcal (Calories) tristearin would be

42 kJ/g x (1 kcal/4.18 kJ) = 42 kJ/g x (1 kcal/4.18 kJ) = 10 kcal/g10 kcal/g

In general carbohydrates and proteins have an In general carbohydrates and proteins have an average fuel value of 4 kcal/g and fats are 9 average fuel value of 4 kcal/g and fats are 9

kcal/g. This is what you see as Calories on food kcal/g. This is what you see as Calories on food labels.labels.

Energy Stored in FuelsEnergy Stored in Fuels

Octane (2,3,5 trimethyl pentane, Octane (2,3,5 trimethyl pentane, Hº = -255 Hº = -255 kJ/mol)kJ/mol)

2 C2 C88HH18 18 (l) + 25 O(l) + 25 O22(g) (g) 16 CO 16 CO22(g) + 18 H(g) + 18 H22O(g) O(g) HH° = -10,138 kJ° = -10,138 kJ

-10,138 kJ/(2-10,138 kJ/(2114 g/mol) = 114 g/mol) = -44 kJ/g-44 kJ/gEthanol (Ethanol (Hº = -278 kJ/mol)Hº = -278 kJ/mol)

CC22HH55OHOH (l) + 3 O(l) + 3 O22(g) (g) 2 CO 2 CO22(g) + 3 H(g) + 3 H22O(g) O(g) HH° = -1234 kJ° = -1234 kJ

-1234 kJ/(31 g/mol) = -1234 kJ/(31 g/mol) = -40 kJ/g-40 kJ/gMethane (Methane (Hº = -75 kJ/mol)Hº = -75 kJ/mol)

CHCH44(g) + 2 O(g) + 2 O22(g) (g) CO CO22(g) + 2 H(g) + 2 H22O(g) O(g) HH° = -802 kJ° = -802 kJ

-802 kJ/(16 g/mol) = -802 kJ/(16 g/mol) = -50 kJ/g-50 kJ/gHydrogen (Hydrogen (Hº = 0 kJ/mol)Hº = 0 kJ/mol)

2 H2 H2 2 (g) + O(g) + O22(g) (g) 2 H 2 H22O(g) O(g) HH° = -484 kJ° = -484 kJ

-484 kJ/(2-484 kJ/(22 g/mol) = 2 g/mol) = -121 kJ/g-121 kJ/g