A piece of silver at 120 degree C is dropped in 300 g water, water warms from 5

Question

A piece of silver at 120 degree C is dropped in 300 g water, water warms from 5 degree C to 20 degree C, a. How much heat has water absorbed? b. How much heat capacity of silver in J/C? The following equation has Delta H degree f_____(True, False) 1/2 N_2(g) + 1/2 O_2(g) rightarrow NO(g) One of the following is False for Delta H degree f: a. Formed from one mole of its element b. The standard state conditions are 25 degree C and 1 bar c. It's standard heat of formation d. The amount of substance formed is 1 mole

Explanation / Answer

1.

Heat absorbed by water= mass of water* specific heat of water* temperature difference = 300*4.18*(20-5)= 18810 Joules

At equilibrium, silver is also expected to reach 20 deg.c

Hence heat capaicty of silved= 18810/(120-20)= 18810/100= 188.1 J/deg.c

2. the given reaction will have deltaHf, since it is formed from its constituent elements.

in the reaction 1/2N2+1/2O2----->NO, the product is formed from 1/2 mole of N2 and 1/2 mole of O2, hence statement is not true. Rest of the statements are true.

when deltaH is +ve, the reaction is endothermic and when deltaH is -ve, the reaction is exothermic. The units of deltaHf are Kj/mole. deltaH units are in Kj/mole. Hence incorrect.

deltaH= sum of enthalpy of products- sum of enthalpy of reactants

For the reaction, deltaH= 1* deltaHfCaCl2+1* deltaHf water –{ 1* deltaH Ca(OH)2+2* deltaH HCl}

= -795-242-{-987-92)= 42 Kj

1, 1, 1 and 2 are coefficients of CaCl2, water, Ca(OH)2 and HCl.

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