You have a badly tarnished silver teapot. The tarnish is a result of the silver

Question

You have a badly tarnished silver teapot. The tarnish is a result of the silver metal reacting with the oxygen in the air according to 4Ag(s) + O2(g) rightarrow 2Ag2O(s), Delta H = -62.2 kJ/mol You carefully clean the teapot and then, out of curiosity, you weigh it. The teapot has a mass of 975g. After some more measuring and calculating, you also determine that 10.0% of the silver is on the surface and exposed to the air. If the teapot were once again to become completely tarnished, how much mass Delta m is converted to energy? Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

This is the procedure all you need to do is plug in your values. The mass of the teapot is 968g, so we convert this into moles: 968g Ag / 107.8682g Ag/mol = 8.97391446227 moles Ag The problem states that 5.30% gets tarnished, so we have to find out how many moles are tarnished: 8.97391446227 moles Ag * 0.0530 = 0.47561746650031 moles Ag tarnished We are given the enthalpy of the Rxn to be -62.2kJ/mol, however we want to just find the information about Ag, so since there are 4 Ag we can divide the ?H / 4 -62.2/4 = -15.55kJ/mol Ag -15.55kJ * 0.47561746650031 moles Ag tarnished = -7.39585160 kJ * 1000J = -7395.85160 J Now we can use E=mc2 -7395.85160 = m * (3*108)2 m = -8.21761*10-14 kg m = -8.21761e-11 g You would lose +8.21761*10^-11 grams.

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