Thermochemistry of Phase Changes

Key Questions

• How can I solve thermochemistry changes of state/phase problems?

  When a compound is changing phase, i.e. it is in a phase transition, it is in equilibrium. That means #DeltaG_"trs" = 0#. So:

  #cancel(DeltaG_"trs") = DeltaH_"trs" - T_"trs"DeltaS_"trs"#

  #color(blue)(DeltaH_"trs" = T_"trs"DeltaS_"trs")#

  If there was more you were looking for to your answer, please clarify.

  Truong-Son N. · 1 · Nov 20 2015
• Why is thermochemistry important?

  Enthalpy change for an aqueous solution can be determined experimentally. Utilizing a thermometer to measure the temperature change of the solution, (along with the mass of the solute) to determine the enthalpy change for an aqueous solution, as long as the reaction is carried out in a calorimeter or similar apparatus . You can use a coffee cup calorimeter.

  1. Measure the mass of solute in grams using a balance. I am dissolving solute Sodium Hydroxide. The mass I have taken is 4 g or 0.1 moles.

  2. Measure the volume of water. I am going to use 100 ml of water. Record the Density of water. Using Density and volume of water I can calculate the mass of water using formula; --> Mass = Volume x Density (let us assume the density of water to be 1g / ml, the mass of 100 ml of water is 100g.

  3. Pour the 100 ml of water in a coffee cup calorimeter, record the temperature of water , the initial temperature of water is #27^o# C.

  4. Add 4 g of Sodium Hydroxide to the water. Dissolve the sodium Hydroxide using a stirrer and also record the temperature of solution. Let us assume that the final temperature of the solution is #48^o# C

  5. In this dissolution experiment Sodium hydroxide dissolves in water and gives off heat energy to the surrounding water , which causes the temperature of water to go up from #27^o# C to #48^o# C. The change in temperature is #48^o# C - #27^o# C = #21^o# C

  6. Use the formula Q = mass of water . specific heat of water . change in Temperature to calculate amount of heat gained by water.

  7. Q = 100 g . 4.18 J / #g^oC#. #21^o# C

  Q = 8778 J or 8.778 kJ

  Water has gained 8.778 kJ of heat energy from the salt, or salt has lost 8.778 kJ of heat energy to water. So energy lost by salt is -8.778 kJ.

  Change in enthalpy = Q lost by salt / # of moles of salt

  = -8.778 kJ / 0.1 mol = -87.88 kj /mol

  Manish Bhardwaj · 1 · Nov 26 2014
• How is thermochemistry used for phase changes?

  Answer:

  Thermochemistry is used to calculate the amount of energy required to change from state to state.

  Explanation:

  For example, if you need to change from solid water to liquid, there is a constant known as heat of sublimation (specific heat), which has been experimentally determined. However, there is a constant for all liquids and that can be derived with simple algebra. Without making things complicated, here is a table to help guide you:

  

  Aidan Bradley · 1 · Jun 5 2018

• How much energy is required to convert 100.g of ice at 0.00 °C to water vapor at 100.00 °C?
• How do you calculate the heat required to melt 15 kg of silver?
• When a liquid loses energy, will it change into a gas or a solid?
• What is the name of the process when a liquid changes into a gas?
• How much energy is needed to convert 23.0 grams of ice at -10.0°C into steam at 109°C?
• What amount of ice must be added to 540.0 g of water at 25.0 °C to cool the water to 0.0 °C and have no ice?
• How can I find specific heat in thermochemistry of phase of changes?
• How much energy is required to convert 100.0 g of water at 20.0 °C completely to steam at 100.0 °C?
• Calculate the number of joules given off when 32.0 grams of steam cools from 110.0 °C to ice at -40.0 °C.
• How many joules of heat are needed to change 50.0 grams of ice at -15.0 °C to steam at 120.0 °C?
• What amount of energy is used when 33.3 grams of ice at 0.00 °C is converted to steam at 150.0 °C?
• How can I solve thermochemistry changes of state/phase problems?
• How many kJ are required to heat 45.0 g of H2O at 25.0°C and then boil it all away?
• What amount of heat is needed to raise 27.0 g of water from 10.0 °C to 90.0 °C?
• How can I calculate thermochemistry equations for phase changes?
• How can I calculate "q" thermochemistry?
• How is thermochemistry used in my freezer?
• How is thermochemistry used for phase changes?
• What are some common mistakes students make in thermochemistry?
• What is an example of a thermochemistry practice problem?
• What is thermochemistry?
• Question #42ee6
• Question #45474
• Question #c6520
• Question #464e1
• Question #cf9b5
• Question #20be5
• A 154 g sample of water at 0oC freezes into ice at °C How many joules (J) of energy are needed for the phase change?
• Question #2bf52
• Question #4329b
• Question #1c02e
• Question #1c1c5
• Question #2a1c5
• Question #2a6cb
• Question #05480
• Question #d6e4b
• Question #7ab5e
• Calculate the amount of heat that must be released to convert 20.0 g of mercury vapor at #387^@"C"# to liquid mercury at #307^@"C"# (in kJ)?
• Calculate the amount of heat (in kJ) that must be absorbed to convert 108 g of ice at #0^@"C"# to water at #70^@"C"#?
• Assume 12,500 J of energy is added to 2.0 moles of #H_2O# as an ice sample at #0^@"C"#. The molar heat of fusion is 6.02 kJ/mol. The specific heat of liquid water is 4.184 J/g K. The remaining sample consists of?
• Question #1112a
• How do you use the equation for heat flow at constant temperature and pressure (latent heat of fusion or vaporization)? #q = nDeltaH#
• Question #f8771
• Question #c7976
• Question #da803
• Question #4fbf8
• What are the 1st and 2nd laws of Thermodynamics?
• How would you find the molar enthalpy of vaporization for a substance, given 3.21 mol of the substance absorbs 28.4 kJ of energy as heat when the substance changes from a liquid to a gas?
• Why boiling point of a liquid remain constant although heat is continuously supplied to the liquid?
• How much heat is necessary to vaporize 500 g of water at its boiling point?
• How much heat is required to boil 83.0 g of water at its boiling point?
• As water is cooled, at what temperature do its particles become fixed?
• The latent heat of vaporization of water is #2260# #J##/##g#. How many kilojoules per gram is this, and how many grams of water will vaporized by the addition of #2.260*10^3# #J# of heat energy at #100°C#?
• What amount of heat is required to completely melt a 29.95-gram sample of #H_2O(s)# at 0° C?
• What happens when you add heat to matter? What about when you take it away?
• Suppose a bag full of ice (450 g) at 0.0 °C sits on the counter and begins to melt to liquid water. How much energy must be absorbed by the ice if 2/3 of it melted?
• What amount of heat is required to completely melt a 29.95-gram sample of #H_2O#(s) at 0° C?
• What is the enthalpy required to vaporize #"63.5 g"# of water at #100^@ "C"#? #DeltabarH_"vap" = "40.66 kJ/mol"#.
• Question #8a0c8
• What is the minimum amount of heat required to completely melt 20.0 grams of ice at its melting point? A. 20.0J B. 83.6J C. 6680J D. 45,200J How do you solve
• Question #3a2df
• Question #98d79
• Question #9fc6b
• Question #e02ea
• The molar heat of fusion for water is 6.01 kJ/mol. How much energy is released when 36.8 g of water freezes at its freezing point?
• What is the heat released when 25.0 grams of water freezes at 0°C?
• Question #d87ef
• How much heat (in kJ) is absorbed when 24.8 g #H_2O(l)# at 100°C and 101.3 kPa is converted to steam at 100°C?
• Because the freezing point and the melting point of water are the same and the heat of fusion is 6 kJ/mol, it takes 6 kilojoules to either freeze or melt a mole of water. What is wrong with this statement?
• What is the amount of heat required to change one gram of a liquid into a gas without changing its temperature?
• How much heat input in #"kJ"# is required to produce #"450 g"# of water vapor from liquid water?
• Question #121e9
• Question #a3360
• What is the energy released by 20 grams of 100°C steam that condenses and then cools to 0°C?
• Question #ad235
• How much energy is released when 16.5 g of steam is condensed at 100°C if the heat of vaporization is 2260 J/g?
• In a calorimeter, 1.0 kg of ice melts at 0°C. The enthalpy of fusion of the ice is 334 J/g. How much heat was absorbed?
• How much heat is required to melt 52.8 g of water?
• In a calorimeter, 10.0 g of ice melts at 0°C. The enthalpy of fusion of the ice is 334 J/g. How much heat was absorbed?
• Question #f5a12
• What is the heat in kilojoules needed to vaporize 9.00 kg of water at 100°C?
• How do you calculate the heat in joules needed to freeze 295 g of water at 0*C?
• How much energy is needed to vaporize 0.22 kg of water?
• Question #35f15
• Question #7a804
• How many joules does it take to melt 35 g of ice at 0° C?
• Question #09ac6
• Which is more effective at raising the boiling point of a soup? Why? SrBr2 Ca3N2 KCl CH4
• How many kilojoules of heat are required to melt 325 grams of ice?
• What is the minimum amount of energy released in kilojoules when 450.0 grams of water vapor condenses to a liquid at 100°C?
• A sample of #H_2O# with a mass of 46.0 grams has a temperature of 100°C. How many joules of energy are necessary to boil the water?
• How much heat is required to take 100. g of ice at 0.00 C to steam at 115 C?
• How many joules of heat are required to melt a 55.0-g ice cube at 0°C?
• How much energy is required to melt 1.5 kg of lead?
• Question #2db9c
• Use the following data to calculate the energy required to convert 10.0 g of liquid water at 100.0C to steam at 115.0C under a constant 1 atm pressure.?
• A 315 g sample of water is heated until it has completely melted. How much heat energy was used?
• Why is there no change in the temperature when the process of melting takes place?
• What is the total number of joules released when a 5.00-gram sample of water changes from liquid to a solid at 0.0°C?
• Question #fe189
• What are the limitations of the first law of thermodynamics?
• How does the first law of thermodynamics affect your life?
• How do you prove the first law of thermodynamics?
• How can you violate the first law of thermodynamics?
• What is the first law of thermodynamics in simple terms?
• What is a reaction that releases heat referred to as?
• What happens when the products of a reaction are hotter than the reactants?
• Ethanol, #CH_3CH_2OH#, has a vapor pressure of 59 mm Hg at 25 °C. What quantity of energy as heat is required to evaporate 125 mL of the alcohol at 25 °C?
• What amount of heat is required to melt #"300 g"# of ice at its freezing point if the enthalpy of fusion is #"6.02 kJ/mol"#?
• Question #70251
• Question #8b463
• What is the energy associated with the phase transition of a #2311*g# block of ice at #0# #""^@C# to WATER at the SAME TEMPERATURE?
• Question #70282
• Question #c8d5a
• Question #8b4c0
• Question #8b4e9
• What does #DeltaH_f# stand for?
• How much heat is required to vaporize 80.6 g of water at 100 C? The heat of vaporization of water at 100 C is 40.7 kJ/mole.?
• How much heat was transferred in this process?
• You are boiling potatoes on a gas stove, and your friend suggests turning up the heat to cook them faster. Will this idea work?
• What mass of water would release 16700J of energy when freezing?
• Question #183ce
• Can you provide the thermodynamic data to show why #"HF"# is such a weak acid compared to #"HI"#?
• Does temperature increase during melting?
• To melt the ice on your driveway, you can use two moles of rock salt (#NaCl#) or two moles of calcium chloride (#CaCl_2#) which solute will have the greatest effect and why?
• Question #cddb2
• A35.8 g sample of cadmium metal was melted by an electric heater providing 4.66 J/s of heat. If it took 6.92 min from the time the metal began to melt until it was completely melted, what is the heat of fusion per mole of cadmium?
• What is the relationship between oxygen use and heat production?
• What is the term for heat transfer because of the movement of a gas?
• If a sealed syringe that contains some gas is heated, in which direction will the syringe plunger move?
• If the mass of a test tube with copper oxide before heating is 30g and the mass of the test tube with copper after heating is is 20g, what was the mass of the oxygen heated off?
• How do changes in temperature affect the particle motion of a substance?
• What is the enthalpy of the phase transition ice to water with respect to a #20*g# mass of ice?
• #1)# What is the change in internal energy of combustion in #"kJ/mol"# for a bomb calorimeter whose heat capacity is #"3024 J/"^@ "C"# that has raised in temperature by #1.2910^@ "C"# due to the combustion of #"0.1575 g Mg"#? Also help with one more?
• Question #a9795
• Question #48544
• Question #30924
• How much heat is produced when 29.6 g of methanol react with 45.9 g of oxygen?
• Question #4e396
• The heat of vaporization of water is 40.66 kJ/mol. How much heat is absorbed when 2.87 g of water boils at atmospheric pressure?
• Question #638a4
• If you are forming a snowball with your bare hands, what is the direction of heat flow?
• If the net #DeltaH# is zero, is the reaction an endothermic or exothermic process?
• How much energy is required to heat a #10*g# mass of ice and give water at #20# #""^@C#?
• What energy is necessary to heat #10*g# of ice at #-10# #""^@C# to give #10*g# steam at #100# #""^@C#?
• Question #483cf
• A 10-lane Olympic-sized swimming pool contains #2 x 10^6# kg of water. If the water is at 0°C, how many kilojoules of energy must be removed to freeze the water in this pool? #DeltaH_(fus)# for #H_2O# = 334 J/g
• Question #02123
• At which Celsius temperature does lead change from a solid to a liquid?
• At what Celsius temperature does mercury change from a solid to a liquid?
• The lattice energy for sodium iodide is 700 kJ/mol, while that for calcium sulfide is 2775 kJ/mol. Which of these salts do you predict has the higher melting point?
• What are the values of #DeltaH# and #DeltaS# for the change from gaseous to liquid #H_2O#?
• At what Celsius temperature does lead change from a solid to a liquid?
• Which phase transition requires more heat, melting or freezing, if the mass of water/ice in both cases is #"35.0 g"#?
• What is the change in the freezing point of water when 35.0 g of sucrose is dissolved in 300.0 g of water?
• What is the total amount of heat required to completely melt 347 grams of ice at its melting point?
• What is the temperature at which a substance changes from a solid to a liquid?
• Question #44dab
• At what temperatures is water a gas?
• Is water freezing to ice an exothermic or endothermic process?
• The latent heat of fusion for ice is 6.0 kJ/mole. In order to melt 36 g of ice (solid #H_2O#) at 0°C, how much energy is required?
• When a solid melts, is thermal energy removed from the solid?
• How much heat is evolved when 122 g water freezes to solid water (ice) at its freezing point?
• Question #55c1b
• Question #605f9
• Question #939e5
• What is the temperature at which a solid freezes called?
• Question #e7912
• How much energy is required to raise the temperature of 3 g of silver from 15°C to 20°C?
• What is #DeltaH# in the equation #DeltaG = DeltaH - TDeltaS#?
• Does the type of liquid affect how fast an ice cube melts?
• What energy is required to melt a block of ice at #0# #""^@C#, and raise the temperature of the water to #10# #""^@C#?
• In the heating curve for water shown below, why is line WX longer than line YZ?
• Question #b91ab
• What is the freezing point of a solution that contains 0.550 moles of #NaI# in 615 g of water?
• Question #65b8b
• Question #27012
• What happens as water freezes?
• In the heating curve, heat is applied to a solid substance at a constant rate. What accounts for the fact that segment CD is longer than segment AB?
• Question #fb2c9
• As a 6 kg of a liquid substance at its freezing point completely freezes , it gives enough heat to melt 3 kg of ice at #0^o# C the heat of fusion of the substance is ?
• Question #9db85
• How much heat is needed to vaporize #"25.0 mL"# of water at its normal boiling point? #DeltaH_(vap) = "40.65 kJ/mol"#.
• The molar heat of fusion of iron is #14.9# kJ/mol. What is the energy (in kJ) needed to melt #4.50g# of iron?
• The heat of vaporization of water is 2260 J/g. How do you calculate the molar heat of vaporization (J/mol) of water?
• The heat of vaporization of water is #2260# #Jg^-1#. How do you calculate the molar heat of vaporization #(Jmol^-1)# of water?
• Water freezes at what temperature in Celsius?
• The heat of vaporization of alcohol is 879 #Jg^-1#. What is the energy (in J) required to vaporize #4.50# #g# of alcohol, #C_2H_5OH#?
• The heat of vaporization of alcohol is 879 J/g. What is the energy in J required to vaporize 4.50 g of #C_2H_5OH#?
• How much heat must be removed to freeze a tray of ice cubes at 0C? The mass of the water is 225 g?
• How much heat is absorbed when 52.3 g #H_2O#(l) at 100 C and 101.3 kPa is converted to steam at 100 C? The molar heat of vaporization of water is 40.7 kJ/mol.
• During a phase change, what happens to the temperature of a substance?
• How is the temperature of a substance affected as it undergoes a change of state?
• What is the mathematical equation showing that the quantity of heat absorbed by vaporizing is the same as the quantity of heat released when the vapor condenses?
• What is needed to calculate the amount of heat absorbed as a substance melts?
• How much heat must be removed to freeze a tray of ice cubes if the water has a mass of 40.0 g? (The molar heat of fusion of water is 6.02 kJ/mol.)
• How much heat is needed to convert 10 grams of ice at 0°C to water at 0°C?
• What is an everyday example of freezing point depression?
• A piece of solid wax is placed in pan and heated on a stove. After a while, the solid wax becomes a liquid. Why does the wax become a liquid?
• In a cup of liquid water, when would the water molecules stop moving?
• A sample of #H_2O# with a mass of 46.0 grams has a temperature of 100 C. How many joules of energy are necessary to boil the water? (Use 2.0934 J/g for the heat of vaporization of water)
• Question #2ca27
• Question #319f9
• Question #20bb9
• Question #6cb54
• Question #fc739
• Question #550ac
• Question #3de10
• What is the vapour pressure of water?
• What is the heat flow involved for #"250 mL"# of water that freezes? #DeltaH_f = "6.02 kJ/mol"#. Assume the density of water is #"1.00 g/mL"# at this temperature.
• Question #067de
• Question #35b3b
• Question #b01e8
• Question #387cd