What Are the Individual Masses of Silver and Gold Used to Convert Ice to Steam?

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SUMMARY

The discussion focuses on a thermodynamics problem involving the conversion of ice to steam using 20 grams of silver and gold. The individual masses of silver and gold were calculated using the heat transfer equations Q1=Q2, Q=mCpΔT, Q=mLvap, and Q=mLfus. The initial calculations led to an incorrect mass of gold due to erroneous values for the heat of fusion and heat of vaporization, which were corrected by multiplying by 103. The final mass of gold was determined to be 0.027 kg, which is consistent with the constraints of the problem.

PREREQUISITES
  • Understanding of thermodynamics principles, specifically heat transfer.
  • Familiarity with specific heat capacities (Cp) of materials.
  • Knowledge of phase changes, including heat of fusion and heat of vaporization.
  • Ability to solve algebraic equations involving multiple variables.
NEXT STEPS
  • Review the concept of heat transfer in thermodynamics.
  • Study specific heat capacities of various materials, focusing on metals like silver and gold.
  • Learn about phase change calculations, particularly heat of fusion and heat of vaporization.
  • Practice solving thermodynamic problems involving multiple substances and phase changes.
USEFUL FOR

This discussion is beneficial for students studying thermodynamics, particularly those tackling heat transfer problems in chemistry or physics. It is also useful for educators looking for examples of common mistakes in thermodynamic calculations.

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Homework Statement


Twenty grams of silver and gold (total mass of the gold plus the silver is 20 grams) is used to convert 1 g of ice at -3°C to steam at 100°C. If both the silver and the gold are at their melting points at the beginning and the final temperature of the silver, gold and steam is 100°C, what was the individual mass of the silver and the gold?

Homework Equations


Q1=Q2
Q=mCpΔT
Q=mLvap
Q=mLfus

The Attempt at a Solution


mAu= x kg
mAg= (.02-x) kg
mice= .001 kg
ΔTAu= 1064-100 = 964
ΔTAg= 962-100 = 862
CpAu = 130 J/kg\cdotC°
CpAg = 230 J/kg\cdotC°mAuCpAuΔTAu + mAgCpAgΔTAg = miceCpiceΔTice + miceLfus + mwaterCpwaterΔTwater + mwaterLvap
x(130)(964) + (0.02-x)(230)(862) = (0.001)(2100)(3) + (0.001)(333) + (0.001)(4186)(100) + (0.001)(2260)
125320x + 3965.2 - 198260x = 6.3 + 0.333 + 418.6 + 2.26
-72940x = -1980.5
x = 0.027 kg

My answer is over 0.02 kg (20g) and because I'm solving for the mass of gold, it was to be less than 20 grams. I've done this problem about four times already and I know I'm doing something wrong, I just can't figure out what.
Any help is greatly appreciated, thank you!
 
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Look at the largest term on the right, it dominates,

(0.001)(4186)(100) = 418

and make the left side as small as possible,

x(130)(964) + (0.02-x)(230)(862) --> .02*130*964 = 2500

The problem as stated is wrong or your values are wrong?
 
@Spinnor --thank you! I figured out what was wrong --both my values for heat of fusion and heat of vaporization were wrong --I had to multiply them each by 103 to get the right answer, whoops! Thanks for the help though!
 

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