Energy Change in Reactions

Key Questions

• What causes energy changes in chemical reactions?

  The energy change that occurs as the result of a reaction depends on the difference between the energy of the reactants and the energy of the products.

  For reactions like combustion, the fuel (for example wood) has energy stored in the chemical bonds between the atoms that make it up. When the wood burns and forms carbon dioxide and water, it releases some energy in the form of heat and light, while some remains stored in the bonds of carbon dioxide and water.

  For some reactions, the products end up with more energy than the reactants (like when we might roll a car uphill). The energy change is still just a measure of the difference between the enrgy of the products, and the energy of the reactants.

  Dr_P · 4 · Apr 11 2014

• Why do endothermic reactions happen?
• What causes energy changes in chemical reactions?
• How do endothermic reactions absorb heat?
• How can endothermic reaction be spontaneous?
• How do I relate equilibrium constants to temperature change to find the enthalpy of reaction?
• What happens to particles when a substance gains energy and changes state?
• For an isothermal process, S = __________?
• If you seal the end of a syringe and push on the plunger, is that process isothermal? If so, explain why. If not, explain what you might do to make it isothermal?
• What is the difference between adiabatic process and isothermal process?
• During an isothermal process, 5.0 J of heat is removed from an ideal gas. What is the change in internal energy?
• Can the entropy of an ideal gas change during an isothermal process?
• What is the enthalpy change for an isothermal process?
• How would you explain an isothermal process?
• Why is an isothermal process slow?
• How can we calculate #DeltaS# for an isothermal process?
• How do you calculate the change in entropy for an isothermal process?
• How do you calculate work for isothermal processes?
• How do you find heat in isothermal processes?
• How do you find q for isothermal processes?
• What is an isothermal process with an example?
• Why is change in enthalpy zero for isothermal processes?
• If 6.00 moles of a monatomic ideal gas at a temperature of 235 L are expanded isothermally from a volume of 1.26 L to a volume of 4.08 L. How would you calculate the work (W) done by the gas?
• What is the amount of energy needed to start a chemical reaction?
• What is the energy level necessary to enable a reaction to occur called?
• 3A chemical reaction produces 653 550 kJ of energy as heat in 142.3 min. What is the rate of energy transfer in kilojoules per minute.?
• How can melting point determinations be used in identifying and/or characterizing unknown compounds?
• What will happen if there is no effective collision and low activation energy of reactants?
• Breaking bonds such as those in Hydrogen peroxide gives off energy What was some proof that energy was released during this experiment?
• What chemical reactions release energy?
• How much energy must be transferred to raise the temperature of a cup of coffee (250 mL) from 20.5 C (293.7 K) to 95.6 C (368.8 K)? Assume that water and coffee have the same density (1.00 g/ mL), and specific heat capacity 4.184 J/ gK)?
• A particle has more than enough energy to eject an electron from a metal's surface. What happens to the excess energy?
• What are the two types of energy changes that can occur in a chemical reaction?
• Question #49509
• What is the Second law of thermodynamics. How would you express it mathematically?
• What are four examples of changes of energy?
• What is one example of change of energy?
• A student performs a neutralization reaction involving an acid and a base in an open polystyrene coffee-cup calorimeter. How would the calculated value of #DeltaH# differ from the actual value if there was significant heat loss to the surroundings?
• How do you calculate the energy absorbed when #2.0x10^3g# of ice (#CO_2#) sublimate at the normal dry sublimation point? The enthalpy of sublimation 196.3J/g.
• The metabolism of one mole of glyceryl trioleate, #C_57H_104O_6#, a common fat, produces #3.510 ×10^4# kJ of heat. How many grams of the fat must be burned to raise the temperature of 50 g of water from 25.0C to 30.0C?
• How can you best describe the transfer of heat that occurs when 1.40 mol of #H_2# reacts?
• How much heat will be released when 12.0 g of #H_2# reacts with 76.0 g of #O_2# according to the following equation? #2H_2 + O_2 -> 2H_2O# #DeltaH#= -571.6 kJ?
• Is condensing water vapor an exothermic process or an endo process?
• A light emitting diode (L.E.D.) emits photons with an energy of #2.84 xx 10^-19# J. What is the energy per mole of photons emitted?
• Is cooling hot water an exothermic process or an endothermic process?
• On a hot day a friend suggests that you can make your kitchen cooler by leaving the refrigerator door open. Would leaving the refrigerator door open cause the air temperature in the kitchen to decrease?
• How do you calculate the #DeltaH# for the combustion of #C_2H_5OH#?
• A 55.0-g aluminum block initially at 27.5 C absorbs 725 J of heat. What is the final temperature of the aluminum?
• How do you calculate the amount of heat (in kJ) required to heat 4.14 kg of water from 21.50 C to 33.85 C.?
• What are chemical reactions that absorb energy?
• Two 20.0-g ice cubes at -11.0 °C are placed into 265 g of water at 25.0 C. Assuming no energy is transferred to or from the surroundings, how do you calculate the final temperature of the water after all the ice melts?
• Where does the energy to heat water for hot chocolate originally come from?
• How could you determine that a liquid has transferred thermal energy to the air?
• How do you calculate the energy needed to heat water?
• What is a reaction that releases energy as it occurs classified as?
• Is this reaction endothermic or exothermic? Gas burning in a Bunsen burner: #C_2H_6(g) + 3.5O_2(g) -> 2CO_2(g) + 3H2O(g) + 2855kJ#
• If the energy level of the products is higher than that of the reactants is the reaction endothermic or exothermic?
• Is the entropy change positive or negative for this reaction? #2KClO_4(s) -> 2KClO_3(s) + O_2(g)#
• Does heat transfer by convection happen mostly in solids, liquids, or gases?
• Why is the dissolution of anhydrous copper sulfate exothermic, and the dehydration of #CuSO_4*5H_2O# endothermic?
• How do you determine the heat of formation of hydrogen peroxide from the given bond energies: #H_2(g) + O_2(g) -> H_2O_2(g)#? Bond energies: H-H = 432; O2 = 494, O-H = 459. O-O = 142?
• Describe what would happen to the temperature of water if a person poured 2 liters of water at 25 degrees C into a container that has 2 liters of water at 75 degrees C. What temperature would the mixture become?
• When exposed to equal amounts of heat energy, copper wams faster than the granite because the two materials have different what?
• Why are told that a sample of matter gives energy as it changes. Can you conclude type of change occurred? Why or not?
• For which phase change does water absorb the most energy?
• Given the balanced equation representing a reaction: #H_2 -> H + H#. What occurs during this reaction?
• If 100.00 J are added to 20.0 g water at 30.0°C, what will be the final temperature of the water?
• Consider the equation #X(g) + en ergy -> X^+ + e^-#. What does the "energy" represent in this equation?
• You have two cups full of liquid. Cup A ls 100 degrees C. Cup B is 20 degrees C. What is the difference in the kinetic energy of the molecules in each cup?
• How much energy, in kilojoules, are released or absorbed from the reaction of 1 mole of #N_2#, nitrogen, with 3 moles of molecular hydrogen, #H_2#, to form 2 moles of ammonia, #NH_3#?
• Is the synthesis of ozone, #O-3#, from oxygen, #O_2#, an example of an exothermic or endothermic reaction?
• What process transfers heat by moving particles from one place to another?
• What process transfers heat by electromagnetic waves?
• Given #2CO(g) + O_2(g) rarr 2CO_2(g)# #DeltaH^@=-564*kJ*mol^-1#...what is the enthalpy associated with the formation of a mass of #44.0*g# of carbon dioxide by these means?
• Why are lakes and oceans are able to stabilize air and land temperatures?
• When a 500. gram sample of water at 19.0 deg C absorbs 8.40 kiloJoules of heat, what will the temperature of the water change to?
• What kind of energy can see and sometimes feel as heat?
• How would I convert kinetic energy for one particle in six dimensions (x, y, z, and their time derivatives) from Cartesian to spherical coordinates? Note: #dotq = (delq)/(delt)#, and this is from a 1962 Statistical Mechanics textbook by Norman Davidson.
• How much heat is lost from a block of solid gold when 2000 g of this gold (Au) cools from 1064 degrees C to 25 degrees C? (Cp(Au) = 0.128 J/g*degC)
• 25.5 g of liquid Benzene (#C_6H_6#) loses 200 J of heat as it cools. What is the temperature decrease?
• Is paper burning with a bright flame endothermic or exothermic? Plastics becoming brittle after being left in the sun? A firecracker exploding?
• What are the four forms of energy that may be absorbed or released during a chemical reaction?
• What direction does heat move?
• What happens when a beaker containing a solution of lithium chloride is heated?
• Is water freezing to ice endothermic or exothermic? Natural gas burning?
• Chemists commonly use a rule of thumb that an increase of 10 K in temperature doubles the rate of a reaction. What must the activation energy be for this statement to be true for a temperature increase from 25 to 35°C?
• Question #538c9
• Student A drops 3 metal washers at 75 deg C into 50 ml of 25 deg C water and student B drops 3 metal washers at 75 C into 25 ml of 25 C water. Which student will get a greater change in the temperature of the water? Why?
• Given the following, how do you calculate #K_c# for the reaction #2C Cl_4(g) + O_2(g) rightleftharpoons 2COCI_2(g) + 2Cl_2(g)#?
• How do you calculate the energy change of reaction for the following reaction?
• When electricity is produced from coal, the chemical energy in coal is first changed to what type of energy?
• This is an example of heat transfer by what?
• Given the balanced equation representing a reaction: #2NaCl -> 2Na + Cl_2#. What must happen to energy in the reaction to break the bonds in NaCl?
• What is the value for #Delta G# at 5000 K if #DeltaH# = -220 kJ/mol and #DeltaS# = -0,05 kJ/(mol*K)?
• What does positive #DeltaH# tell about a reaction?
• What conditions make #DeltaG# always positive?
• Thermal energy added to a substance during a change of state causes the substance's temperature to do what?
• What is a device that can change chemical energy into electrical energy?
• What is the transfer of energy through empty space called?
• Question #77483
• Question #af81a
• Question #ee0ca
• Question #27e59
• When heat is transferred between objects of different temperatures, what is the end result?
• What is a process that absorbs heat?
• How much heat is released when 2.00 kg of aluminum solidifies? How many kJ is this?
• Will lowering the temperature raise the energy level of the particles?
• Water vapor condensation on the outside of a water bottle. Endothermic or exothermic and why?
• Sweat evaporates off your arm. Endothermic or exothermic and why?
• Which reaction of those listed is MOST exothermic?
• Is the dissolution of a gas in a solvent exothermic?
• Why is the joule, the SI unit of energy, also the appropriate unit for measuring heat?
• Question #842f0
• When 168 joules of heat is added 4 grams of water at 283 K, what is the resulting temperature?
• How much heat does 32.0 g of water absorb when it is heated from 25.0 to 80.0 °C?
• What is the number of joules of heat energy released when 20 grams of water is cooled from 293 K to 283 K?
• How much energy is released when a 40.0 g sample of liquid water completely freezes at 0 °C?
• What is the study of the changes in the energy that accompanies chemical reactions and physical changes?
• How much heat must be removed to freeze a tray of ice cubes at 0 C if the water has a mass of 225 g?
• How much heat must be removed to freeze a tray of ice cubes at 0°C if the water has a mass of 225 g?
• What happens to particles when you add heat energy?
• Question #595a5
• What is heat transfer through the motion and mixing of molecules?
• Consider the following reaction: #2Mg(s) + O_2(g) -> 2MgO(s)#, #DeltaH = -1204kJ#. Is this reaction exothermic or endothermic? How do you calculate the amount of heat transferred when 2.4 grams of Mg(s) reacts at constant pressure?
• Copper oxide reacts much faster with acid at 40°C than at 20°C. Why is this?
• Fill in the blanks? Word bank color endothermic energy enthalpy exothermic less mass more products reactants grams heat of reaction heat of solution moles negative neutral positive solvent temperature
• How do we assess the enthalpy change in phase transitions?
• Question #824c4
• How much energy is absorbed if 5 kg of aluminum is heated from 10-20 degrees C? (c of aluminum is 900 J/Kg)?
• Question #56e71
• What happens to the kinetic energy of its molecules as ice melts into water?
• What happens to the molecules in matter when you raise the temperature?
• Hot coffee in a mug cools over time and the mug warms up. How would you describe the energy in this system?
• How do you calculate the energy released when 24.8 g #Na_2O# reacts in this reaction: #Na_2O(s) + 2HI(g) -> 2Nal(s) + H_2O(l)#?
• Question #001b0
• How to calculate the potential energy of an electron in the #"nth"# shell (also take example #"n=3"# shell) of a copper atom using the Hartree Fock Theory? Also calculate its kinetic energy
• Can energy be created or destroyed?
• What is the difference between an exothermic process and an exothermic reaction?
• What is reaction isotherm? Describe briefly.
• Question #90d81
• Indicate whether each of the ff. reactions is exothermic or endothermic? a) Br2(l)+Cl2(g)→2 BrCl(g) Δ H=29.4kJ
• When gasoline burns, it reacts with oxygen in the air and forms carbon dioxide and water vapour. How does the potential energy of the gasoline and oxygen compare with the potential energy of the carbon dioxide and water vapour?
• Why do green plants need sunlight to perform photosynthesis?
• Question #9dc3c
• What is the energy of gases at #"0 K"#?
• What are the conditions for an exothermic vs. an endothermic reaction?
• How to treat stretch bond to calculate its enthalpy and entropy contribution?