1. a.) Below is a reaction from a demonstration we did early in the semester in

Question

1. a.) Below is a reaction from a demonstration we did early in the semester in which we put Li(s) into water and saw the pH increase , H 2 (g) evolve , and the reaction catch fire . How much heat is released when 28.0 g of lithium metal reacts as shown below?  

2 Li (s) + 2 H 2 O (l) --> 2 LiOH (s) + H 2(g) Delta H = - 222 kJ   

b.) t o measure this enthalpy change . The temperature of a calorimeter whose contents have a total mass of 500.0 g increased from 20.0 C to 49.8 C when 5.00 g of an uncharacterized fuel was burned to completion in the calorimeter . What is H rxn for this combustion reaction? The specific heat of the contents of the calorimeter is 4.184 J/g C and the molecular weight of the fuel is 40.0 g/mol . E xpress your answer in terms of kJ/(mol of fuel).   

Explanation / Answer

1. a) molecular weight of Li = 6 gm

mole of Li here = 28/6 =4.7 mole

standard reaction predics that 2 mole of Li produces 222 kj heat

so, 4.7 mole will produce = 222*4.7 = 1043.4 J heat

b) note: the unit of temperature is not properly visible.

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