Entropy

Key Questions

• When does entropy increase?

  Entropy increases when a system increases its disorder.

  

  Basically, a solid is pretty ordered, especially if it is crystalline. Melt it, you get more disorder because molecules can now slide past one another. Dissolve it, and you get another entropy increase, because the solute molecules are now dispersed among solvent.

  Order of entropy from least to greatest:
  Solid--> Liquid --> Gas

  ChemGuy · 1 · Apr 11 2014
• What is the difference between entropy and enthalpy?

  Answer:

  Example below explaining entropy and enthalpy

  Explanation:

  In a 4 stroke diesel engine, when piston takes the air into cylinder (sucks the air into cylinder) i.e. performing the first or inlet stroke while moving from top to bottom, it fully fills the cylinder with air then comes the turn of compressing this air and this compression is too much (about the ratio of 1:20) as compared with a 4 stroke petrol engine; in this process Entropy is decreased i.e. size of air is decreased without removing heat from the air (while Enthalpy remains same), this decrease in Entropy without decreasing Enthalpy i.e. without dissipating heat somewhere in the surrounding or nearby matter or environment causes a useful rise in the temperature of air about 600 degree centigrade which is more than enough to burn the diesel sprayed at that very time.

  Amjad K. · 109 · Sep 17 2015
• How do you calculate entropy?

  Here are some formulas.

  #ΔS_"total" = ΔS_"univ" = ΔS_"sys" + ΔS_"surr" = q_"sys"/T_"sys" + q_"surr"/T_"surr"#

  where #q# is the heat and #T# is the Kelvin temperature.

  Entropy Change for the System

  #ΔS_"sys" = ΔS_"rxn" = Sigma(n_pS_"products"^"o") – Sigma(n_rS_"reactants"^"o")#

  where #n_p# and #n_r# represent moles of products and reactions.

  Entropy Change for the Surroundings

  #ΔS_"surr" = q_"surr"/T_"surr"#

  #q_"surr" = -q_"sys"#

  #ΔS_"surr" = q_"surr"/T_"surr" = -q_"sys"/T_"surr"#

  Example 1:

  What is #ΔS_"surr"# at 300 K for the reaction

  reactants → products; #ΔH# = 75 kJ

  Solution:

  #ΔS_"sys" = q/T = (75 000" J")/(300" K")# = 250 J/K

  #ΔS_"surr" = q_"surr"/T_"surr" = -(ΔH_"sys")/T_"surr" = -(75 000" J")/(300" K")# = -250 J/K

  Example 2:

  What is #ΔS_"rxn"^"o"# for the following reaction?

  4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g)

  The #S^"o"# values are NH₃ = 193 J·K⁻¹mol⁻¹; O₂ = 205 J·K⁻¹mol⁻¹; NO = 211 J·K⁻¹mol⁻¹;
  H₂O = 189 J·K⁻¹mol⁻¹

  #ΔS_"sys" = Sigma(n_pS_"products"^"o") – Sigma(n_rS_"reactants"^"o")#

  #ΔS_"rxn"^"o" = 4S_"NO"^"o" + 6S_"H₂O"^"o" – 4S_"NH₃" - 5S_"O₂"^"o"#

  #ΔS_"rxn"^"o" = (4×211 + 6 × 189 - 4 × 193 + 5 × 205 )# J/K⁻¹ = 181 J•K⁻¹

  Ernest Z. · 1 · Apr 17 2014

• How does entropy change with pressure?
• How do you calculate entropy?
• How do you calculate entropy change?
• How do you calculate entropy of vaporization?
• Why does entropy increase with an increase in temperature?
• Why is entropy of the universe increasing?
• Can entropy be zero?
• How do free energy and entropy relate?
• When does entropy increase?
• What is the difference between entropy and enthalpy?
• What is an example of entropy from everyday life?
• Does combustion have a negative entropy or positive entropy?
• Question #3a497
• Question #babca
• Question #8bc90
• Question #ea760
• Question #1445a
• Without doing any calculations, determine the sign of ΔSsys and ΔSsurr for each of the chemical reaction. Predict under what temperatures (all, low, or high), if any, the reaction will be spontaneous? C3H8(g)+5O2(g)→3CO2(g)+4H2O(g) #ΔH_"rxn"^o =−2044kJ#
• What is chemical potential?
• How would you define entropy of a system?
• How does entropy relate to chaos theory?
• How is entropy related to osmosis and diffusion?
• Which state of matter has the highest entropy?
• What is an example of increasing entropy?
• What does it mean if a process is enthalpy-driven?
• Why "S" is used as a symbol of entropy?
• Are enthalpy and entropy affected by temperature?
• Which has more entropy: ice, liquid, water, or water vapor?
• How would you define a spontaneous and a non spontaneous process?
• How would you define the concept of equilibrium in terms of free energy and entropy?
• How would you determine if a reaction is entropy driven or enthalpy driven?
• How would you define entropy of a system?
• What is the relationship between enthalpy and entropy?
• What is the opposite of entropy?
• When does entropy increase and when does it decrease?
• How does entropy relate to osmosis and diffusion?
• Which of the following has the lowest entropy: a liquid, a gas, or a crystalline sold?
• Which state of matter has the highest entropy?
• What is a spontaneous reaction?
• Are enthalpy and entropy affected by temperature?
• How would you define the concept of equilibrium in terms of free energy and entropy?
• What is entropy?
• How does entropy change in the following scenarios: (i) a phase change from solid to liquid; (ii) a solid dissolves in a solvent?
• Question #c1a92
• What is the order of entropy with respect to equal numbers of the following substances: #HCl(aq); "salt crystals; carbon dioxide; solid iron"?#
• Explain why spontaneity depends on temperature?
• For an isolated, insulated system for which a gas is allowed to expand, why is the change in entropy for the system nonnegative?
• Question #9802d
• What is entropy of a system?
• What is the definition of entropy?
• What are Megapascals, Entropy and Enthalpy?
• How do you calculate the entropy for a molecule or atom?
• Does entropy increase or decrease during transformation of egg into chicken?
• Why is entropy equal to #q# for a reversible process? What is the difference between reversible and irreversible?
• What is isothermal expansion?
• How would you explain isothermal expansion?
• How do you calculate isothermal expansion?
• What does isothermal expansion mean?
• What is isothermal expansion of a real gas?
• What is isothermal expansion of an ideal gas?
• What is reversible isothermal expansion?
• Why is isothermal expansion reversible?
• Why is q positive in an isothermal expansion?
• How many micro states exist for a molecule?
• How many microstates are there for any given compound?
• What are microstates in chemistry?
• How are microstates formed in chemistry?
• How do you calculate microstates in chemistry?
• How do you calculate the number of microstates a compound has?
• How does volume affect microstates?
• How many microstates are possible for a molecule?
• Why do you need to calculate microstates in chemistry?
• Entropy plays a larger role in determining the Gibbs energy of reactions that take place at what?
• Question #3c9e4
• How do I calculate the new pressure of liquid water using its isothermal compressibility #kappa# and expansion coefficient #alpha#?
• Without using Wolfram Alpha, evaluate #log_10(y) = -138.265#? The answer is not #0#.
• Can someone explain to me the concept of entropy?
• Question #aa25f
• The dissolving of AgNo3 in pure water is represented by AgNo3 --> Ag+ + NO3-. A) Is deltaG for the dissolving of the silver nitrate positive, negative, or zero? Why? B) Is deltaS for the dissolving of the silver nitrate positive, negative, or zero? Why?
• Question #ddcb7
• Question #7b328
• Is Earth itself an open or closed system?
• Is entropy a state function? How? Prove it?
• #((delS)/(delV))_T = alpha/beta#. Prove this relation please?
• Question #87739
• Question #68b16
• How does the entropy change in the reaction #2C_3H_6(g) + 9O_2(g) -> 6CO_2(g) + 6H_2O(g)#?
• What is entropy the measure of?
• Is a system's work output limited when changes in entropy do not occur?
• What is the value for #DeltaS^o"_(reaction)# for the following reaction, given the standard entropy values? #Fe_2O_3(s) + 3H_2(g) -> 2Fe(s) + 3H_O(g)#
• What would cause entropy to decrease in a reaction?
• Question #885c3
• Question #57ac0
• What is the molar entropy of a system with 150000 microstates at a certain temperature?
• What is the entropy change for the isothermal expansion of #"0.75 g"# of #"He"# from #"5.0 L"# to #"12.5 L"#?
• How do you find the change in entropy of vaporization for water?
• Calculate the change in entropy when #"1 mol"# of argon gas is heated from #"300 K"# to #"1200 K"#, assuming that #C_P = "20.8 J/mol"cdot"K"# and is constant in the temperature range?
• What is the entropy change at #"273 K"# when a perfect gas is compressed at #"1 bar"# to a volume of #"0.011 m"^3# at #"10 bar"#?
• What is reversible heat flow, and how is it related to entropy? What is the difference between reversible and irreversible heat flow?
• Given the distribution of #N# particles in #n# systems, #t = prod_N prod_i (n!)/(n_(N_i)!)#, and the following constraints, derive the grand canonical partition function and the distribution law for the grand ensemble?
• How do you calculate the entropy change in the surroundings when 1.00 mol #N_2O_4(g)# is formed from #NO_2(g)# under standard conditions at 298 K?
• Are entropy values for substance grater than or equal to zero?
• Is entropy state function?
• Is entropy zero for elements under standard conditions?
• Is the entropy of a substance in the gas phase greater than in the solid phase?
• How would you calculate the standard entropy change for the combustion of methanol at 25 C? #2CH_3OH(lamda) + 3O_2(g) -> 2CO_2(g) + 4H_2O(g)#
• How can the entropy of a pure solid to be zero?
• Question #2d5bf
• Why entropy is not zero while free energy of formation of element in its standard form is zero?
• For the hypothetical reaction #A_((g)) rarr B_((g)) + C_((g))#, if the volume is held constant, would entropy increase or decrease? Help please!
• Which of the following processes shows a decrease in entropy of the system?
• How to calculate the change in the entropy of hydrogen molecule before and after the adsorption?
• If given: #Sn(s) + Cl_2(g) -> SnCl_2(s)#, #DeltaH = -325 kJ# and #SnCl_2(s) + Cl_2(g) -> SnCl_4(l)#, #DeltaH = -186 kJ#, what is #DeltaH# for this reaction? #Sn(s) + 2Cl_2(g) -> SnCl_4(l)#
• Given the options, and entropy data, which gives the correct #DeltaS^@_"rxn"# for the reaction.... #2NH_3(g)rarrN_2(g)+3H_2(g)# #"A. -299"*J*K^-1*mol^-1# #"B. -199"*J*K^-1*mol^-1# #"C. +199"*J*K^-1*mol^-1# #"D. +99"*J*K^-1*mol^-1#?
• Which of the following is true about entropy?
• Question #168d2
• How does the entropy change in the reaction #2C_3H_6(g) + 9O_2(g) -> 6CO_2(g) + 6H_2O(g)#?
• Question #aed03
• As glucose is oxidized to carbon dioxide, does the level of entropy increase?
• What causes the entropy to change when a solute dissolves in a solvent?
• For which phase is entropy lowest? Highest?
• For the reaction #2"C"(gr) + "O"_2(g) -> 2"CO"(g)#, what are the changes in entropy of the system, surroundings, and universe at #"298 K"#? #DeltaH_(rxn)^@ = -"221.0 kJ"# at this temperature and #"1 atm"#.
• How many different ways can you distribute three indistinguishable particles in a 3 x 3 ensemble of distinguishable boxes?
• Why does energy preferentially spread out in an isolated system?
• Question #0dfa9
• Which of the following processes would be expected to have a positive #Delta"S"# value?