Chapter 5 Flashcards
Energy
Capacity to do work (w) or transfer heat (q)
Kinetic energy (Ek)
Energy due to particle motion and temperature of sample
Potential energy (Ep or Eel)
Energy due to particles’ position
Kinetic energy equation
KE = (1/2)mv^2
Potential energy equation
Eel = (kQ1Q2)/d
Thermodynamics
The study of energy and its transformations
Thermochemistry
The study of chemical reactions and the energy changes that involve heat
Heat (q)
Energy transfer that results from temperature difference
Work (w) (Physics)
A force applied across a distance
Work (w) (physics) equation
W = F • d
Work (w) (chemistry)
A force done by an expanding gas at a constant pressure
Work (w) (chemistry) equation
W = -P(delta V)
Change in volume equation
Delta V = Vf - Vi
Internal energy (E)
Kinetic + potential energy in a sample
Change in energy equation
Delta E = Ef - Ei
Delta E = q + w
Unit of energy
Joule (J)
System
Portion of the universe we study. To chemists, it is typically the chemical reaction.
Surroundings
The rest of the universe except the system under study
1st law of thermodynamics
Change in universe = 0, so -system = surroundings
Closed system
Energy, but not matter, can be transferred between system and surroundings
Open system
Energy and matter can be transferred between system and surroundings
Isolated system
Energy and matter cannot be transferred between system and surroundings
Potential energy is lowest when…
The particles of matter are attracted and close together, where a negative PE is positive and the most stable
When PE = 0
Particles are neither repelled nor attracted. There is no interaction.
Breaking a chemical bond…
Always requires energy
Forming a chemical bond always…
Releases energy
If delta E is positive (Ef > Ei)…
Esys has gained energy from Esurr
If delta E is negative (Ef < Ei)…
Esys has given energy to Esurr
Endothermic reaction
System gains heat (q is positive)
Exothermic reaction
System loses heat (q is negative)
Work of the system is positive when…
Surroundings work on system (volume decreases)
Work of system is negative when…
System works on surroundings (volume increases)
q (subscript p)
The heat gained or lost under these conditions of constant pressure
q (subscript p) in relation to enthalpy equation
Delta H = q (subscript p)
Enthalpy is a _________ property
Extensive; if you double the amount of matter, the delta H is doubled
Reversing a reaction…
Changes the sign (+ or -) of delta H
The state (s, l, g) of reactants & products are _________
Important; will change overall change in enthalpy of a reaction
Because delta H is a state function, the total enthalpy change for a chemical reaction depends only on…
The initial state of the reactants and the final state of the products
Calorimetry
Experiment to measure heat transferred between system and surroundings (closed system)
Heat capacity (C)
The amount of heat required to raise an object’s temperature by 1K
Heat capacity equation
C = q/delta T
C = Cs • m
Specific heat (Cs)
The amount of heat required to raise 1 gram of object’s temperature by 1K
Specific heat equation
Cs = q/(m•delta T)
A large value for specific heat means…
More heat required to raise temperature and temperature of substance is not easily changed
3 equations for the signs of q
-q lost = q gained
-q sys = q surr
-q rxn = q solution
If the thermometer records a temperature increase…
Heat went into the surroundings, heat left the system (reaction), process is exothermic, and q rxn = delta H rxn = negative
If the thermometer records a temperature decrease…
Heat left the surroundings, heat went into the system, process is endothermic, and the q rxn = delta H rxn = positive
Delta T equation
Delta T = Tf - Ti
Change in enthalpy of a reaction equation
Delta H rxn = q rxn/moles
Two types of calorimeters
Coffee cup: reactions at constant pressure and bomb: reactions involving gases
Equation for calculating q for a bomb calorimetry
q rxn = -q cal = -C cal • delta T
Standard enthalpy of formation (delta H°f)
Enthalpy change for formation of 1 mol of a substance from its elements in their most stable form with all reactants and products at 1 atm pressure and 298 K
Bond enthalpy
The energy it takes to break a typical bond (+ energy)
