11. CRQs of Thermochemistry

S.No	Question	SLO#
1	How are  the standard enthalpies of an element and of  a compound determined?
2	What is meant by standard enthalpy of a reaction?
3	State Hess’s law .Explain with one example ,the usefulness of Hess’s law in thermochemistry?
4	Describe how chemist use  Hess’s law to determine the ∆ Hf of a compound by measuring its heat(enthalpy) of combustion.
5	In writing thermochemical equations, why is it important to indicate the physical state of substance?
6	Write an expression for the enthalpy of reaction in terms of the enthalpies of product and reactant. Under what condition is the heat of reaction is equal to the enthalpy of reaction?
7	Explain what is meant by a state function. Give two example of quantities that are state function and two are not
8	At constant pressure in which of the following reaction is the work done by the system on the surrounding? And work done by surrounding on system? in which of them is no work done? a)      Hg(l)→Hg(g) b)      3O2(g)→2O3(g) c)      CuSO4.5H2O(s) →CuSO4(s)+5H2O(l) d)     H2(g) +F2 (g) → 2HF(g)
9	The internal energy of an ideal gas depend only on its temperature .Do a first law analysis of the following process .A sample of an ideal gas is allowed to expend  at constant  temperature  against  atmospheric pressure . a)      Does the gas do work on its surroundings? b)      Is there heat exchange between the system and the surroundings? If so ,in which direction? c)      What is ∆E for the gas for this process?
10	A gas expend and does work on the surrounding equal t0 325 J .At the same time, it absorb 127 J of heat from the surrounding .Calculate the change in internal energy of gas.
11	Calculate the work done when 50.0 g of tin are dissolved in excess acid  at 1.00 atm  and 250C  Sn(S) +2H+(aq) → Sn2+(aq) + H2(g)   Assume  ideal behavior.
12	Calculate the standard enthalpy of change  for the reaction 2Al(s) + Fe2O3(s) →2Fe(s) +Al2O3 (s) Given that 2Al(s) + 3/2 O2(g) → Al2O3 (s)  ∆H=-1601kJ 2Fel(s) +3/2 O2(g)  →Fe2O3 (s)  ∆H=-821kJ
13	What is the difference between specific heat  and heat capacity? What are the unit for these two quantities ? which is the intensive property and which is the extensive property ?
14	A piece of sliver of mass 362 g has heat capacity of 85.7 J/0C  .What is the specific heat of silver?
15	A 6.22 kg piece of copper metal is heated from 20.5 0C to 324.3 0C .Calculate the heat absorbed(in kJ) by the metal.