Unit 3 Chem - thermodynamics Flashcards
Heat and Energy:
Heat is the transfer of thermal energy between substances due to temperature differences. Energy, in various forms, is exchanged during chemical reactions, influencing the system’s behavior.
Enthalpy Changes:
Enthalpy change represents the heat flow at constant pressure. Exothermic reactions release energy, while endothermic reactions absorb energy
Calorimetry:
the science of measuring the change in heat of chemical reactions or physical changes
the change in temp of the “surroundings” can be measured (the temp of water in can)
the assumption is that no heat is being transferred
Collision Theory:
This theory explains that for a reaction to occur, particles must collide with sufficient energy and proper orientation. Effective collisions lead to successful reactions.
Potential and Kinetic Energy:
Potential energy is stored energy due to position or composition, while kinetic energy is the energy of motion. Chemical reactions involve conversions between these energy forms.
Phase Transitions:
Endothermic processes absorb energy (e.g., melting), while exothermic processes release energy (e.g., freezing). These changes affect the molecular arrangement and energy state.
Exothermic Reaction:
This type of reaction releases heat into its surroundings, resulting in an increase in the temperature of the surroundings. During an exothermic reaction:
The energy released when new bonds form in the products is greater than the energy required to break the existing bonds in the reactants.
Forming bonds releases energy as it involves the atoms coming together and forming more stable configurations, often resulting in the release of heat.
This released energy contributes to the overall decrease in potential energy or increased stability of the products compared to the reactants.
The net result is that the reaction releases excess energy, usually in the form of heat, to the surroundings.
Endothermic Reaction:
This type of reaction absorbs heat from its surroundings, resulting in a decrease in the temperature of the surroundings. During an endothermic reaction:
The energy required to break the bonds in the reactants is greater than the energy released when new bonds form in the products.
Breaking bonds requires an input of energy, often in the form of heat, to overcome the attractive forces holding the atoms together in the reactants.
The absorbed energy goes into breaking the existing bonds in the reactants and, sometimes, to initiate the reaction or cause a phase change, resulting in products with higher potential energy or less stability.
As a result, the products generally have higher potential energy or are less stable compared to the reactants.
activation energy:
activation energy is the minimum collision energy required for a successful reaction to occur
How temp affects rate of reaction
it increases speed so it increases the number of collisions (and probability of reactions
increases number of particles that have sufficient energy (activation energy) and number of particles colliding shifts (to right if hotter, and to left if colder)
Enthalpy of formation
add up enthalpy of formation of all products * moles of each
& subtract the enthalpy of all reactants by n of each
elements have zero enthalpy
usually answers r negative
Hess’s lawww
certain reactions cannot be measured by calorimetry (slow, complex, hazardous)
so we can break up the reaction into several intermediate steps to determine their enthalpy change
The enthalpy change of a multi step reaction is the SUM of the enthalpy changes of the individual steps
BEWARE OF STATES :(
endo vs exo
endo has +KJ for H
exo has -KJ for H
molar enthalpy of combustion
determined when 1 mol of compound is burned at SATP
its n*deltaH comb
enthalpy of state change
during a state change, temp stays constant as all the energy is added or released goes into breaking/forming intermolecular forces
Q=m * deltaH
(deltaHvap, cond, melt)
so when u calc it’s Q=mcT of each STATE + the state CHANGE
ex: Qtot= Qsolid + Qmelting + Qliquid
what are factors that affect heat capacity?
state and IM forces - different states of matter posses diff heat capacity due to the strength
heat capacity
the ability of a substance to RESIST changes in temperature.
the more an atom can u rotate and vibrate and store energy, the more resistant it will be to increasing temperature and the higher the heat capacity
