ch 5 thermochemistry

Question 1

thermodynamics

Answer 1

study of energy and its transformations. Thermochemistry: relationships between chemical reactions and energy changes

Question 2

energy definition

Answer 2

capacity to do work or to transfer heat

Question 3

kinetic energy3

Answer 3

energy of motion. Ek=1/2mv2. m=mass, v=velocity. Kinetic energy increases as speed increases. Atoms/molecules have mass and are in motion=have kinetic energy

Question 4

potential energy2

Answer 4

energy by virtue of position relative to other objects. Arises when there is a force (push or pull) acting on an object. Ep=mgh. m=mass, g=gravitational constant=9.8m/s2. h=height

Question 5

electrostatic potential energy4

Answer 5

arises from interaction between charged particles. Eel is proportional to the electrical charges on the two interacting objects and inversely proportional to the distance between themEel=(kQ1Q2)/d. k=constant of proportionality, =8.99*109J–m/C2. (C =coulomb, unit of electrical charge. J=joule). When Q1 and Q2 have the same sign, they repel one another, and Eel is positive. When they have opposite signs, they attract and Eel is negative.Lower energy of system=more stable.

Question 6

SI unit for energy3

Answer 6

Joule, J. 1J=1kg–m2/s2. Energy associated with chemical reactions is kilojoules.

Question 7

non SI unit for energy4

Answer 7

calorie (cal)=amount of energy to raise temperature of 1g of water from 14.5ºC to 15.5ºC. 1 cal=4.184J. 1Cal=1000cal=1 kcal

Question 8

closed system

Answer 8

can exchange energy but not matter with its surroundings, does not lose or gain mass

Question 9

work2

Answer 9

energy used to cause an object with mass to move. w=F*d

Question 10

heat

Answer 10

energy used to cause the temperature of an object to increase. Transferred from hot object to cold objects

Question 11

first law of thermodynamics

Answer 11

energy is conserved. Any energy lost by the system must be gained by the surroundings, and vice versa.

Question 12

internal energy defs

Answer 12

sum of all kinetic and potential energies of components of system. Represented as E. When E is positive=system gained energy from surroundings. When E is negative=system lost energy to surroundings. Initial state=reactants, final state=products.

Question 13

internal energy formulas2

Answer 13

E=Eproducts-Ereactants

E=q+w.

Question 14

endothermic3

Answer 14

system absorbs heat. (melting of ice). Feels cold because heat transferred from our hands (surroundings) to system. E>0

Question 15

exothermic3

Answer 15

system loses heat. (combustion). Feels hot as temp of system drops and enters surroundings.
E<0

Question 16

state function

Answer 16

property of a system that is determined by the specifying the system’s condition/state. Value of state function depends only on present state of system, not on path system took to reach that state

Question 17

pressure-volume work3

Answer 17

work involved in the expansion or compression of gases. When pressure is constant, w=-PV. P=pressure, V=change in volume (Vfinal-Vinitial). When volume expands, V is positive and w is negative, meaning energy leaves system as work and vice versa for when a gas is compressed.

Question 18

enthalpy5

Answer 18

thermodynamic function that accounts for heat flow in processes occurring at constant pressure when no forms of work are performed other that P-V work. Denoted by symbol H.
H=E+PV.
H=E+PV=(qP+w)-w=qp. qp emphasizes changes at constant pressure.
Change in enthalpy =heat gained/lost at constant pressure
H>0(meaning when qP>0), heat is gained=endothermic

Question 19

enthalpy of reaction/heat of reaction

Answer 19

Hrxn=Hproducts-Hreactants

Question 20

thermochemical equations

Answer 20

balanced equations that show the associated enthalpy change where the coefficients represent the number of moles of reactants/products producing the associated enthalpy change.

Question 21

enthalpy diagram

Answer 21

another way of representing enthalpy change through a diagram. If reaction is exothermic, reactants are written higher than products with an arrow drawing down to indicate loss of heat

Question 22

facts about enthalpy change5

Answer 22

The enthalpy change of a reaction is equal in magnitude but opposite in sign to H for the reverse reaction.
When H is large and negative, it is spontaneous/thermodynamically favored
When H is large and positive, it is spontaneous in the reverse direction
Gases have greater internal energy than liquids, so if liquids were changed to gas on the reactant side, H would decrease but if liquid changed to gas on product side, H would increase

Question 23

calorimetry

Answer 23

measurement of heat flow. Calorimeter: device used to measure heat flow

Question 24

heat capacity2

Answer 24

represented as C, the temperature change experienced by an object when it absorbs a certain amount of heat. Amount of heat required to raise its temperature by 1 K (or 1ºC). Greater heat capacity, the greater the heat required to produce a given increase in temp

Question 25

molar heat capacity

Answer 25

Cmolar, heat capacity of one mole of a substance.

Question 26

specific heat3

Answer 26

heat capacity of 1g of a substance. Represented as s.
s=q/(mT).
q=sm*T

Question 27

coffee cup calorimeters4

Answer 27

since they are not sealed, the reaction occurs under constant pressure of the atmosphere.
Heat gained/lost by the reaction (system) must be gained/lost by the solution(surroundings). qsoln= -qrxn. qsoln=ssolnmsolnT=
-qrxn.
A temp increase(T>0) in the solution means the reaction is exothermic (qrxn<0)

Question 28

bomb calorimeters5

Answer 28

combustion reactions.
Substance to be studied is placed in a small cup within a sealed vessel called a bomb which can withstand high pressures.
Bomb is sealed and pressurized with oxygen and placed in insulated container (calorimeter) when a measured quantity of water.
Combustion reaction occurs, causing water temp to rise. qrxn=-Ccal*T. (Ccal is total heat capacity of calorimeter)
Because reactions in bomb calorimeters are carried out out under constant volume conditions, heat transferred corresponds to change in internal energy, E, rather than change in enthalpy, H

Question 29

hess law

Answer 29

if a reaction is carried out in a series of steps, Hfor the overall reaction will equal the sum of the enthalpy changes for the individual steps.
H is the same whether the reaction takes place in one step or in a series of steps

Question 30

enthalpy of formation/heat of formation

Answer 30

Hf, enthalpy change associated with formation of a compound from its elements. Subscript f indicates the substances has been formed from its component elements.

Question 31

standard state

Answer 31

state of a substance at its pure form at atmospheric pressure, 1 atm, and 25ºC/298 K. Standard enthalpy change of a reaction is the enthalpy change when all reactants and products are in their standard states. Denoted as Hºwhere superscript º indicates standard-state conditions

Question 32

standard enthalpy of formation

Answer 32

Hºf, is change in enthalpy for the reaction that forms one mole of the compound from its elements, with all substances in their standard states. They are reported in kJ/mol. Each reactant is an element in its standard state and product is one mole of the compound.
The standard enthalpy of formation of the most stable form of any element is zero because there is no formation reaction needed when the element is already in its standard state.

Question 33

standard enthalpy of reaction formula

Answer 33

Hºrxn= { nHºf(products)-
{ mHºf(reactants). = { sum of, n and m=stoichiometric coefficients of the chemical equation. First term represents formation reactions of products written in forward direction (elements reaction to form products), second term represents reverse of formation reactions of reactants (reactants decompose to form elements)

Question 34

fuel value

Answer 34

energy released when one g of a material is combusted. Reported as positive numbers
Greater percentage of C and H in a fuel=higher its fuel value

Question 35

fossil fuels

Answer 35

coal, petroleum, natural gas which have formed over millions of years from decomposition of plants and animals and are being depleted faster than being formed, nonrenewable

Question 36

natural gas

Answer 36

gaseous hydrocarbons

Question 37

petroleum

Answer 37

liquid composed of hundreds of compounds, mostly hydrocarbons

Question 38

coal

Answer 38

solid, contains hydrocarbons of high molecular weight
Coal gasification: coal is pulverized and treated with superheated steam a produces mixture of gaseous hydrocarbons (syngas)

Question 39

nuclear energy

Answer 39

energy released in either splitting or fusion of nuclei of atoms, nonrenewable. Produce radioactive waste products

Question 40

renewable energy

Answer 40

solar, wind, geothermal, hydroelectric, biomass energy