Chem Chapter 5

(delta)H =

(Delta)(E+PV) = (Delta)E +P(Delta)V (P is constant) = q(p) + w - w = q(p) The p after q indicates that the process occurs at constant pressure. Thus, the change in enthalpy equals the heat q(p) gained or lost at constant pressure.

Pressure-volume work with constant pressure

(or P-V work) is work that is a result of a volume change against an external pressure. when gases expand, deltaV is +, but the system is doing work on the surroundings, so w is negative. w = -P * (delta)V Where w = work, P = pressure, and (delta) V = change in volume.

endothermic processes

+(delta)H: temp of surroundings will decrease

exothermic processes

-(delta)H: temp of surrounding will increase

1st law of thermodynamics (conservation of energy)

-energy is neither created nor destroyed -energy of the universe is constant -energy can be transferred between objects -energy can be transformed from one form to another (heat to light, kinetic energy to potential, or potential to kinetic)

atmospheric pressure

1 atm

1 J =

1 kg-m^2 / s^2 This is because KE = 1/2(mv^2) = 1/2 (2kg) (1m/s)^2 =1kg-m^2/s^2

guidelines for thermochemical equations and enthalpy

1. Enthalpy is an extensive property. The magnitude of (delta)H is proportional to the amount of reactant consumed in the process. 2. The enthalpy change for a reaction is equal in magnitude, but opposite in sign to (delta)H for the reverse reaction 3. The enthalpy change for a reaction depends on the state of the reactants and products

1. Radiant energy 2. Thermal energy 3. Chemical energy 4 Nuclear energy

1. comes from the sun and is earth's primary energy source (kinetic energy) 2. the energy associated with the random motion of atoms and molecules (kinetic energy) 3. the energy stored within the bonds of chemical substances (potential energy) 4. the energy stored within the collection of neutrons and protons in the atom (potential energy)

1 calorie =

4.184 J (exactly) (also the amount of energy needed to raise one gram of water by 1 degree Celsius)

state function

A function that depends only on the initial and final states of a system, not on the path in between. Internal energy (E), Pressure (P), Volume (V), and Enthalpy (H) are all state functions (along with delta of all of these).

endothermic

A process in which the system absorbs heat

closed system

A system that allows for the exchange of energy, but not matter, across its boundaries.

open system

An open system is a system that can freely exchange matter and energy with its surroundings.

q (heat) =

C X (delta)T C is the heat capacity ( J/degrees Celsius or J/Kelvin) delta T is the change in temperature of the system

kinetic energy

Energy of motion

potential energy

Energy stored due to an object's position or arrangement

work =

Force * Distance object moves

Work and is it extensive or intensive?

Force acting over a distance or force X distance. A force is any push or pull exerted on an object. Extensive

magnitude of kinetic energy (on eq sheet)

KE = 1/2 * (mv^2) KE = magnitude of kinetic energy m = mass v= velocity

molar heat capacity eq

Molar heat capacity = (quantity of heat transferred) / (number of moles X temperature change) C(m) = (q) / ((n) X (deltaT))

isolated system

No exchange of heat, work, or matter with surroundings

heat capacity

The amount of heat required to raise the temperature of a specified amount of a specified substance substance by 1°C or 1 K.

enthalpy of reaction or heat of reaction

The enthalpy change that accomponies a reaction, sometimes written (delta)H(rxn) where rxn is an abbreviation for reaction. By convention, we calculate enthalpy change for the number of moles of reactants in the reaction as written

Enthalpy

The heat content of a system at constant pressure H = E +PV Where H is enthalpy, E is internal energy, P is pressure, and V is volume

thermodynamics

The study of energy and its transformations

thermochemistry

The study of energy changes that occur during chemical reactions and changes in state

constant volume calorimetry with bomb calorimeter

When volume is constant, w=-p(delta)V v= 0 So w = 0 that means (delta)E = q + 0 This means, with a constant volume and insulated surroundings, we can directly measure (delta)E using q.

thermochemical equations

a balanced chemical equation that includes the physical states of all reactants and products and the energy change that accompanies the reaction

calorimeter

a measuring instrument that determines quantities of heat

exothermic

a process in which the system loses heat

algebraic expression of 1st law of thermodynamics (deltaE =)

change in internal energy of system = q + w w = work q= heat

any change is always...

directional. It is always final minus initial. For example, the change in energy is always final energy - initial energy

Is enthalphy of reaction an extensive or intensive property?

extensive, the more reactants you use the larger the magnitude of the enthalpy change

non state functions

heat and work

heat capacity equation

heat capacity = quantity of heat transferred / change in temperature C = q / (delta)T

Internal energy, E, of a system...

is the sum of all the kinetic and potential energies of the components of the system

change is enthalpy is always given in

kJ

calorimetry

measurement of heat flow

change in energy of system =

negative change in energy of surroundings because change in internal energy = final energy (energy of reactants) - initial energy (energy of products) the surrounding then either gets an equal amount of energy taken away from it (if final energy is greater than initial) or added to it (if final energy is less than initial) energy flow from the system to the surroundings is always negative (loss of energy from the system) energy flow from the surroundings to the system has a positive sign (gain of energy to the system)

calculating q given enthalpy of reaction

number of moles of given substance X enthalpy of reaction/coef of given substance from balanced equation

system in a reaction

reactants and products

formation reactions

reactions of elements in their standard state to form 1 mole of a pure compound -If you are not sure what the standard state of an element is, find the form in the appendix that has a standard change in enthalpy = 0 for that element. -Since the definition requires one mole of compound be made, the coefficients of the reactants may be fractions

fusion

solid to liquid phase change

calculating q given specific heat

specific heat = (quantity of heat transferred) / (grams of substance X temperature change) OR C(s) = (q) / ((m) X (delta)T) Therefore q= (m) X (Cs) X (delta)T

standard enthalpy change of reaction from tabulated standard enthalpy of formation values equation

standard enthalpy of reaction = the sum of all ( n * standard enthalpy of formation of products) - the sum of all (n * standard enthalpy of formation of reactants) where n is the number of moles of a certain product or reactant in the balanced equation.

standard state

state of material at a defined set of conditions pure gas at exactly 1 atm pure solid or liquid in its most stable form at exactly 1 atm pressure and temperature of interest (usually 25 degrees celcius)

difference between temperature and heat

temperature is a measure of average thermal energy of the atoms in a substance and is an Intensive property. Heat is the transfer of thermal energy between two bodies that are a different temperature and is an extensive property. For example, if you were to heat 2 containers of water, one much larger than the other, to 100 degrees Celsius, they would both have the same temperature, but the larger container would have much higher thermal energy. This is because the amount of energy that had to be transferred to the larger container to raise it to 100 degrees celcius is larger than the amount of energy that had to be transferred to the smaller container. another way to think of it is, (sum of the energies of each atom)/ number of atoms = temperature. So, for the larger container to be 100 as well, the sum of the energy of the atoms must have been grater in the larger container.

energy

the capacity to do work or transfer heat

Hess's law

the change in enthalpy for a stepwise process is the sum of the enthalpy changes of the steps

standard enthalpy change of formation

the enthalpy change for a reaction forming one mole of a pure compound from its constituent elements - the elements must be in their standard states -the change in elthalpy of formation for a pure element in its standard state is 0 kJ/mol

standard enthalpy change

the enthalpy change when all reactants and products are in their standard states

specific heat

the heat capacity of one g of a substance

molar heat capacity

the heat capacity of one mole of a substance

heat and is it extensive or intensive?

the transfer of thermal energy between two bodies that are at different temperatures. Extensive property

reactions done in aqueous solutions open to the atmosphere are

under constant pressure

units obtained by P-V work and conversion to joules

units of pressure (usually atm) multiplied by units of volume (usually liters). To express work in joules, the conversion factor 1 L-atm = 101.3 J is useful.