Heat Unit Exam
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Exothermic
Heat energy is a PRODUCT/result of the reaction occuring. -> Heat is RELEASED Feels warm In these reactions, products have LESS energy than the reactants because the energy has been released.
Endothermic
Heat energy as a REACTANT/is necessary for the reaction to occur. -> Heat is absorbed from the surroundings Feels cool Products have MORE energy than reactants because energy has been absorbed.
Conversion from kj to J
1000J = 1kj
if delta H is negative…
The reaction is EXOTHERMIC (releasing energy)
if delta H is positive…
the reaction is ENDOTHERMIC (absorbed)
Kinetic Molecular Theory
All matter is made up of tiny particles that attract each other and contain kinetic energy.
Kinetic Energy
the energy of motion. –> All particles in any substance are in motion.
Temperature
The average kinetic energy of particles in a substance. Hotter = faster particles
Celcius
based on pure water at sea level • Freeze at 0 degrees • Boil at 100 degrees
Kelvin
standard in science based on molecular notion kelvin to celsius = degree C + 273
Thermal Energy
the total amount of potential and kinetic energy contained in the particles of a substance. -> Determines how fast particles move. —-> Determines how hot or cold
Heat vs Temp
HEAT is the transfer of energy TEMP is the measure of energy
Conduction
One thing physically touches another and heats it through direct contact. -> Solids
Convection
Forms convection currents as heat is transferred through fluids. -> Liquid & Gas
Radiation
Heat is transferred through electromagnetic waves.
Q=mc(Tf-Ti)
• ONE object • Information about TEMPERATURE, MASS, HEAT CAPACITY, and/or ENERGY REQUIRED
Thermal Heat Exchange
When two objects come into contact, the hotter object will slowly transfer heat energy to the cooler object until they reach the same temperature. –> Amount of energy lost = energy gained
-mc(Tf-Ti) = mc(Tf-Ti)
• TWO substances/objects • Thermal heat exchange • ONE final temperature
Volume Expansion - When you warm an object…
The particles inside will move slightly further apart, causing the object/substance to increase in size, and vice versa.
Volume Expansion vs Linear Expansion
When an object is heated, it will begin to expand in ALL directions. In objects that are long and thin, only the linear (length) expansion is significant.
3 Things that impact Linear Expansion
1) Length of Material 2) Change in Temperature 3) Type of Material
When to use linear expansion formula…?
The question will say something about linear expansion or length.
When to use volume expansion formula…?
Use common sense - if the question does not explicitly say volume, it should be pretty obvious.
Melting/Fusion
Solid -> Liquid Liquid -> Solid