Level 69 Level 71
Level 70

Heats of Reaction

112 words 0 ignored

Ready to learn       Ready to review

Ignore words

Check the boxes below to ignore/unignore words, then click save at the bottom. Ignored words will never appear in any learning session.

All None

Define Energy
is the ability to do work (move mass over a distance) or transfer heat
Internal energy (E)
the sum of the kinetic and potential energy for each particle in the system
by moving particles
How can energy be transferred?
The collision of fast moving molecules with slower molecules will cause what?
the slow molecules to speed up while the fast molecules to slow
Precisely where an object is located
When does potential energy increase?
when objects that attract move apart or when objects that repel move toward each other
stored energy
What can be converted to kinetic energy?
Define the First Law of Thermodynamics
Energy cannot be created or destroyed, but can be transformed from one form of energy to another
In terms of energy define temperature
of an object is proportional to the average kinetic energy of its particles—the higher the average kinetic energy, the higher the temperature
Define heat
is energy (also called thermal energy) transferred between objects caused by differences in their temperatures until they reach thermal equilibrium
What is temperature propotional to?
is proportional to the average kinetic energy of all particle units: °C, °F, K
Give the units for energy
SI unit is the Joule, J
? E = Eproduct - Ereactant = 0
1st Law of Thermodynamics: For an isolated system the internal energy (E) is constant:
What is E
a state function
Define state function
A property whose value depends only on the present state of the system, not on the method or mechanism used to arrive at that state
heat transfer during a reaction
Give an example of a state function
Heat Transfer (q)
the transfer of energy from regions of high temperature to regions of lower temperature
The region of interest when some change in energy, reaction, etc. is being studied, ex. a flask of gas, a beaker of acid.
all parts of the universe other than the system being considered.
open systems
can gain or lose mass and energy across their boundries
closed systems
can absorb or release energy, but not mass across the boundry
A chemical reaction that absorbs heat
A chemical reaction that releases energy
Define heat capacity
the (extensive) ability of an object with constant mass to absorb heat.
Define Specific Heat
The intensive ability of a substance to store heat.
temperature changes
What do substances with high specific heat resist?
How long does heat transfer contiue?
until thermal equilibrium is reached, thus the final temperature is the same for all materials
Chemical Bond
An attractive force that holds together the atoms, ions, or groups of atoms in a molecule or compound.
In sense of bonds define exothermic
reactions form stronger bonds in the products than in the reactants and release energy
In sense of bonds define endothermic
reactions break stronger bonds than they form and require energy
How does work relate to reactions?
most often due to the expansion or contraction of a system due to changes in moles of gas as a result of a chemical reaction.
Psystem = -Patm
Gases push against the atmospheric pressure , so
Heat of reaction
is the quantity of heat released or absorbed during a chemical reaction.
measures how the heat absorbed or released in a chemical or physical change.
Internal Energy is Measured with a Bomb Calorimeter
Used for reactions in which there is change in the number of moles of gas present
Enthalpy of Combustion
the enthalpy change that occurs during the complete combustion of 1 mole of a substance
always negative
Enthalpy change is
is the heat transferred at constant pressure
pressure to remain constant
What does open system allow?
Thermochemical Equations
Relate the energy of a reaction to the quantities involved
Hess's Law
the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process.
Rules for Adding Thermochemical Reactions
When an equation is reversed—written in the opposite direction—the sign of H must also be reversed.
Strategy for Adding Reactions Together
Choose the most complex compound in the equation (1)
Enthalpy of formation, ?H°f
is the enthalpy change for the formation of 1 mole of a substance in its standard state from elements in their standard states
Enthalpy Change
Another term for the heat of reaction
H2O + heat energy
H+ (aq) + OH- (aq) -->
? T :: ? collisions :: ? rate of reaction
a flow of energy due to a temperature difference
Energy in a substance
Heat in a substance =
Specific Heat
the amount of heat necessary to raise the temperature of 1 gram of a substance by 1 °C
Specific Heat Equation
Q = cm?T
Change in temperature K
Joules (or calories)
The measurement of the energy food gives us
Amount of energy within a system
?H for Exothermic Reactions
The enthalpy of the products is less than that of the reactants so the ?H value will be negative
?H for Endothermic Reactions
The enthalpy of the products is greater than that of the reactants so the ?H value will be positive
Free Energy
The energy that is available to do work
Spontaneous Reaction
Occurs naturally and favors the formation at the stated conditions. They produce large amounts of products and release free energy.
Nonspontaneous Reaction
Does not favor the formation of products at the stated conditions and produce little, if any, product
a change in randomness or complexity
Law of Disorder
States that the natural tendency is for systems to move in the direction of increasing disorder or randomness
Reactions in which entropy increases..
As reactants form products to be favored
activation energy
Energy Diagram's hill bisector line
a substance that increase reaction rate w/o being permanently used up or changed. it lowers the activation energy needed for the reaction so more molecules have the necessary energy for a reaction
Chemical Equilibrium
A reversible chemical reaction when the rate of its forward reaction equals the rate of its reverse reaction and the concentration of its products and reactants remain unchanged
Reversible Reaction
A chemical reaction in which the products can react to re-form the reactants
Le Chatelier's Principle
application of stress (change in temp, pressure, or concentration) on a system at equilibrium causes it to minimize the stress and attain new equilibrium position
Reactions that Go to Completion
This happens when ions are almost completely removed from solution which depends on degree of solubility and degree of ionization
Formation of a Gas
This formation has unstable substances that are formed as products of ionic reactions decompose spontaneously
Formation of a Precipitate
This formation has a reaction that goes to completion because an essentially insoluble product is formed
Formation of a Slightly Ionized Product
In this formation, if water is present, assume that it will go through completion
reaction rate
speed at which chemical reactions occur
chemical kinetics
study of how fast chemical reactions occur
Rate-Influencing Factors
Nature of reactants, surface area, temperature, concentration, presence of catalysts
Heterogeneous Reactions
Involve reactants in two different phases
homogeneous catalyst
a catalyst that is in the same phase as all the reactants and products
heterogeneous catalyst
a catalyst that is in a different phase
oxidation-reduction reactions
In which one or more electrons are transferred are called
addition of oxygen or loss of electrons
Loss of oxygen, gain of electrons
Equilibrium "lies to the right"
because products predominate and products are written on the right-hand side of a chemical equation
When the equilibrium of a system is disturbed....
The system makes adjustments to restore the equilibrium
Change in ... concentration, pressure, and temperature
3 stresses that cause a change in equilibrium
When a reactant is added to a system at equilibrium...
The reaction shifts in the direction of the formation of products
When a reactant is removed from a system at equilibrium...
The reaction shifts in the direction of formation of reactants
The extent to which reactions go to completion depend on...
The solubility of the compound formed, if the compound is soluble, and the degree of ionization
When an insoluble product is formed..
It cannot effectively go through completion
What is organic chemistry?
The study of the compounds of carbon.
Name 3 inorganic compounds of carbon.
Carbon Dioxide, Carbon Monoxide and Carbonate Salts.
What is a hydrocarbon?
A compound that contains only hydrogen and carbon.
What are the alkanes?
Alkanes are a family of hydrocarbons in which all the atoms are linked by single bonds (Saturated).
What is the molecular formula of methane?
What is the molecular formula of ethane?
What is the molecular formula of propane?
What is the molecular formula of butane?
What is the molecular formula of pentane?
What is the molecular formula of hexane?
What is the molecular formula of heptane?
What is the molecular formula of octane?
What is the molecular formula of nonane?
What is the molecular formula of decane?
What is the general formula for all alkanes?
CnH2n+2, where n is the number of carbon atoms.
What is a homologous series?
A series with a uniform chemical type, a general formula for all it's members, similar method of preparation, similar physical properties and each member differs by a CH2 unit.
What are structural isomers?
Compounds with the same molecular formula but different structural formulas.
What is an alkyl group?
An Alkane molecule from which a hydrogen atom has been removed.
What are aliphatic compounds?
Any organic structure with straight us branched chains and no ring structures.
What are aromatic compounds?
Compounds that contain a benzene ring structure.
What are alkenes?
A homologous series which contains a >C=C< double bond, are unsaturated and have a general formula of CnH2n.
What are alkynes?
A highly unsaturated, homologous series with a general formula of CnH2n-2.
Why is Benzene unreactive?
It has a molecular formula of C6H6 which suggest that it would be very reactive. However, upon further examination, it was discovered that benzene had three carbon single and double bonds of intermediate lengths…