Concept explainers
Interpretation:
The standard enthalpy change for the given reactionis to be calculated with the help of given data.
Concept introduction:
Hess’s Law states that the change in enthalpy fora
The enthalpy change for a reaction is a state function. It depends upon the initial and final states of the system and not on the path followed.
If any reaction is reversed, then the sign of enthalpy change will also reverse. If enthalpy change is positive, then it will become negative and vice versa.
If any reaction is multiplied or divided any number, then its enthalpy change is also multiplied and divided by the same number.
Want to see the full answer?
Check out a sample textbook solutionChapter 5 Solutions
ALEKS 360-ACCESS (1 SEMESTER)
- The Romans used calcium oxide, CaO, to produce a strong mortar to build stone structures. Calcium oxide was mixed with water to give Ca(OH)2, which reacted slowly with CO2 in the air to give CaCO3. Ca(OH)2(s) + CO2(g) CaCO3(s) + H2O(g) (a) Calculate the standard enthalpy change for this reaction. (b) How much energy is evolved or absorbed as heat if 1.00 kg of Ca(OH)2 reacts with a stoichiometric amount of CO2?arrow_forwardGasohol, a mixture of gasoline and ethanol, C2H5OH, is used as automobile fuel. The alcohol releases energy in a combustion reaction with O2. C2H5OH(l)+3O2(g)2CO2(g)+3H2O(l) If 0.115 g ethanol evolves 3.62 kJ when burned at constant pressure, calculate the combustion enthalpy for ethanol.arrow_forwardThe standard molar enthalpy of formation of diborane, B2H6(g), cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured. 4 B(s) + 3 O2(g) 2 B2O3(s) rH = 2543.8 kJ/mol-rxn H2(g) + O2(g) H2O(g) rH = 241.8 kl/mol-rxn B2H6(g) + 3 O2(g) B2O3(s) + 3 H2O(g) rH = 2032.9 kJ/mol-rxn (a) Show how these equations can be added together to give the equation for the formation of B2H6(g) from B(s) and H2(g) in their standard states. Assign enthalpy changes to each reaction. (b) Calculate fH for B2H6(g). (c) Draw an energy level diagram that shows how the various enthalpies in this problem are related. (d) Is the formation of B2H6(g) from its elements exo- or endothermic?arrow_forward
- Another reaction that is used to propel rockets is N2O4(l)+2N2H4(l)3N2(g)+4H2O(g) This reaction has the advantage that neither product is toxic, so no dangerous pollution is released. When the reaction consumes 10.0 g liquid N2O4, it releases 124 kJ of heat. (a) Is the sign of the enthalpy change positive or negative? (b) What is the value of H for the chemical equation if it is understood to be written in molar quantities?arrow_forward9.73 Without looking up any numerical data or doing calculations, predict whether the enthalpy change for each of the following reactions should he positive, negative, or zero. (a) H2O(l)H2O(s) (b) N2(g)2N(g) (c) CH4(g)+2O2(g)CO2(g)+2H2O(l) (d) CO2(s)CO2(g)arrow_forwardThe enthalpy change for the following reaction is 393.5 kJ. C(s,graphite)+O2(g)CO2(g) (a) Is energy released from or absorbed by the system in this reaction? (b) What quantities of reactants and products are assumed? (c) Predict the enthalpy change observed when 3.00 g carbon burns in an excess of oxygen.arrow_forward
- Calculate the standard enthalpy of combustion for benzene, C6H6. C6H6() + 15/2 O2(g) 6 CO2(g) + 3 H2O() rH = ? The enthalpy of formation of benzene is known [rH[C6H6()] = +49.0 kJ/mol], and other values needed can be found in Appendix L.arrow_forwardUnder what circumstances is the heat of a process equal to the enthalpy change for the process?arrow_forwardIs the following reaction the appropriate one to use in determining the enthalpy of formation of methane, CH4(g)? Why or why not? C(g)+4H(g)CH4(g)arrow_forward
- The enthalpy of combustion of diamond is -395.4 kJ/mol. C s, dia O2 g CO2 g Determine the fH of C s, dia.arrow_forwardA 0.470-g sample of magnesium reacts with 200 g dilute HCl in a coffee-cup calorimeter to form MgCl2(aq) and H2(g). The temperature increases by 10.9 C as the magnesium reacts. Assume that the mixture has the same specific heat as water and a mass of 200 g. (a) Calculate the enthalpy change for the reaction. Is the process exothermic or endothermic? (b) Write the chemical equation and evaluate H.arrow_forwardWhite phosphorus, P4, ignites in air to produce P4O10. When 3.56 g P4 is burned, 85.8 kJ of thermal energy is evolved at constant pressure. Calculate the combustion enthalpy of P4.arrow_forward
- Chemistry & Chemical ReactivityChemistryISBN:9781337399074Author:John C. Kotz, Paul M. Treichel, John Townsend, David TreichelPublisher:Cengage LearningChemistry: Principles and PracticeChemistryISBN:9780534420123Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward MercerPublisher:Cengage LearningChemistry: The Molecular ScienceChemistryISBN:9781285199047Author:John W. Moore, Conrad L. StanitskiPublisher:Cengage Learning
- Physical ChemistryChemistryISBN:9781133958437Author:Ball, David W. (david Warren), BAER, TomasPublisher:Wadsworth Cengage Learning,Chemistry for Engineering StudentsChemistryISBN:9781337398909Author:Lawrence S. Brown, Tom HolmePublisher:Cengage LearningChemistry & Chemical ReactivityChemistryISBN:9781133949640Author:John C. Kotz, Paul M. Treichel, John Townsend, David TreichelPublisher:Cengage Learning