Unit 5- Thermochem

Question 1

Thermochem

Answer 1

the study of the relationship between heat and chemical reactions

Question 2

kinetic energy

Answer 2

energy possessed by matter bc it is in motion

Question 3

thermal energy

Answer 3

energy in the form of random motion of particles in any sample of matter
- as temp rises, thermal energy inc

Question 4

heat

Answer 4

energy that causes a change in the thermal energy if a sample. Adding heat to a sample increases its temp

Question 5

potential energy

Answer 5

the energy derived from the position or condition of matter

Question 6

chem energy

Answer 6

a form of potential energy derived from the forces that hold the atoms together in a compound

Question 7

system

Answer 7

a sample of matter on which we focus our attention, generally the atoms involved in a CHEMICAL REACTION

Question 8

surroundings

Answer 8

all other matter in universe

Question 9

law of conservation of energy

Answer 9

the energy of the universe is constant during a chem or physical change
(energy may move between the system and surrounding but total energy not changed)

Question 10

exothermic reaction

Answer 10

when the system (atoms involved in rxn) transfers heat to surroundings
- key words: produce, provide, give off, release
- loses energy, Enthalpy neg

Question 11

endothermic reaction

Answer 11

rxn that absorbs heat from surroundings
- key words: need, absorb, require
- gains energy, Enthalpy pos

Question 12

enthalpy

Answer 12

measure of the energy of the SYSTEM

Question 13

change in enthalpy (delta H)

Answer 13

equal to the heat absorbed or given off by the system at constant pressure

Question 14

Thermochem equation

Answer 14

an equation for which enthalpy is given
- enthalpy changes assume that the coeff are MOLEs of the substance (enthalpy/ coeff mole or vice versa)

Question 15

calorimetry

Answer 15

the experimental measurements of heat released or absorbed by a chem rxn

Question 16

calorimeter

Answer 16

the device used to measure heat

Question 17

specific heat (Cs)

Answer 17

the heat needed to inc the temp of 1g of matter by 1k
- units: J/gC or J/gK

heat(q)=mass(m) x Cs x (Tf-Ti)

Question 18

qsurr

Answer 18

deltaH = qsys = -qsurr

Question 19

state fxn

Answer 19

a property of the system that is fixed by the present conditions and is indep of the system’s history
(*enthalpy)

Question 20

path fxn

Answer 20

a property that depends on how the particular change took place

Question 21

Hess’s Law

Answer 21

when 2 or more thermochem eq are added, the enthalpy change of the resulting eq is the sum of those for the added eqs

Question 22

standard state

Answer 22

the pure form of a substance at a specified temp at 1atm pressure
- temp usually 25 deg

Question 23

standard enthalpy of formation

Answer 23

the enthalpy change when 1 molec of a substance in its standard state is formed from the most stable form of its constituent ele in standard states
(deltaH of formation rxn)
-units: KJ/mol

Question 24

standard enthalpy of formation of ELE

Answer 24

0

Question 25

standard enthalpy change of rxn

Answer 25

deltaHf^o = sum n x deltaHf^o [PRODUCTS] - sum n x deltaHf^o [REACTANTS]

n=coeff in eq