Chemistry Chapter 15.1-15.3
Because the reactants are present at the beginning of the reaction and the products are present at the end, 🔼H rxn is defined by the equation...
🔼H rxn = H products - H reactants
Standard enthalpy changes have the symbol...
🔼H^0 The zero superscript tells you that the enthalpy changes were determined with all reactants and products at standard conditions.
The enthalpy change, 🔼H, is equal to...
"Qp", the heat gained or lost in a reaction or process carried out at constant pressure, you can assume that q = 🔼H rxn
Enthalpy (heat) of combustion (🔼H comb)
(Of a substance) is the enthalpy change for the complete burning of one mole of the substance
Specific Heat
(Of an substance) is that amount of heat required to raise the temperature of one gram of that substance by one degree Celsius
Specific Heat of concrete
0.84 J/(g•C)
1 (big) Calorie = 1 (small) calorie
1 (big) Calorie/1000 (small) calories Or 1000 (small) calories/1 (big) Calorie
Nutritional Calorie to calorie
1 Calorie = 1000 calories (or one kilocalorie)
1 J = 0.2390 cal.
1 J/0.2390 cal. Or 0.2390 cal./1 J
Joule to calories & calorie to joules
1 Joule = 0.2390 calories 1 calorie = 4.184 joules
Standard conditions are...
1 atm pressure and 298 K (25 degrees C) and should not be confused with standard temperature and pressure (STP)
1 cal = 4.184 J
1 cal./4.184 J Or 4.184 J/1 cal.
Amount of calories or joules of pure water required to raise the temperature of one gram by one degree Celsius
4.184 J or 1 cal. Or 4.184 J/(g•C)
Thermochemistry equation
A balance chemical equation that includes the physical states of all reactants and products and the energy change, usually expressed as the change in enthalpy, 🔼H
Calorimeter
An insulted device used for measuring the amount of heat absorbed or released during a chemical or physical process
The amount of energy lost or gained can be measured conveniently in a calorimeter at
Constant pressure
The Kinetic Energy of a substance is
Directly related to the constant random motion of its representative particles and is proportional to temperature
Potential Energy
Energy due to the composition or position of an object
Kinetic Energy
Energy of motion
Heat (q)
Energy that is in the process of flowing from a warmer object to a cooler object
Chemical Potential Energy
Energy that is stored in a substance because of its composition
Surroundings
Everything in the universe other than the system
T or F: you CAN measure the actual energy or enthalpy of a substance
False CANNOT
T or F: the energy released or evolved from reactions carried out at constant pressure is sometimes given the symbol "Qs"
False "Qp"
T or F: enthalpy changes for endothermic reactions are always NEGATIVE.
False POSITIVE
Signs of enthalpy: Exothermic
H products < H reactants
Signs of enthalpy: Endothermic
H products > H reactants
What kind of energy transfer occurs during endothermic reaction?
Heat flows from the surrounding to the system
What kind of energy transfer occurs during exothermic reaction?
Heat flows from the system to part of the surroundings
The quantity, "4.184 J/(g•C)"
Is defined as the specific heat (c) of water
When the warmer object loses energy
Its temperature decreases
When the cooler object absorbs energy
Its temperature rises
After the starting signal is given, the skier's potential energy changes to _______ during the speedy trip to the finish line
Kinetic Energy
Thermodynamics
Law of Conservation of Energy
Instead of measuring the actual energy or enthalpy of a substance (which you cannot) you can...
Measure the change in enthalpy, which is the heat absorbed or released in a chemical reaction
The Potential Energy of a substance depends
On its composition: the type of atoms in the substance, the number and type of chemical bonds joining the atoms, and the particular way the atoms are arranged
The position of downhill skier poised at the starting gate for a race
Potential Energy
The burning of fuel always...
Produces heat
Q M C 🔼t
Quantity of heat Mass Calorie Temperature
Virtually every chemical reaction and change of physical state either...
Releases or absorbs heat
Energy
The ability to do work or produce heat.
Calorie (cal)
The amount of energy required to raise the temperature of one gram of pure water by one degrees Celsius
Enthalpy (heat) of reaction (🔼H rxn)
The change in enthalpy for a reaction
🔼H rxn?
The difference between the enthalpy of the substances that exist at the end of the reaction and the enthalpy of the substances present at the start 🔼H rxn = H final - H initial
Enthalpy (H)
The heat content of a system at constant pressure
As temperature increases
The motion of submicroscopic particles increases
System
The specific part of the universe that contains the reaction or process you wish to study
Thermochemistry
The study of heat changes that accompany chemical reactions and phase changes
Universe
The system plus the surroundings
In a foam cup calorimeter, the flow of heat only stops when...
The temperature of the metal and the water are equal
A known mass of water is placed in an insulated chamber...m
To absorb the energy released from the reacting system or to provide the energy absorbed by the system
T or F: Chemists are usually more interested in changes in energy during reactions than in the absolute amounts of energy contained in the reactants and products
True
T or F: enthalpy changes for exothermic reactions are always negative.
True
T or F: it is impossible to know the total energy content of a substance
True
Joule (J)
Unit for "of energy" and "of heat"
Bomb calorimeter
Used by food chemists
