Water at 23.0 °C is sprayed onto 0.140 kg of molten gold at 1063 °C (its melting point). The water boils away, forming steam at 100.0 °C and leaving solid gold at 1063 °C. What is the minimum mass of water that must be used?

Could someone please checking my working out? My answer is incorrect and I'm not sure why.

The answer should be in kg

Water at 230 C is sprayed onto 0140 kg of molten gold at 1063 C its melting point The water boils away forming steam at 1000 C and leaving solid gold at 1063 C class=

Respuesta :

The conservation of energy in calorimetry we can find the amount of water to transform gold from the liquid state to the so

           m = 3.48 10-3 kg = 0.00348 kg

To find

  • The mass of water

Calorimetry analyzes the change in temperature of a body when there is a heat transfer with another body in contact, this is expressed by the related

        Q = m c_e ΔT

Where Q is the thermal energy, m is the mass, c_e the specific heat and ΔT is the temperature variation  

The transformation of the state of matter liquid solid and liquid vapor occurs with changes in temperature, since the energy supplied is used to change the separation of the molecules and change state

           Q = m L

Where m is the mass and L the latent heat  

In this case, the coldest body is the water that, when in contact with the gold, undergoes the following processes  

   • It is heated from the initial temperature (T₀ = 23ºC) to the evaporation temperature (T_f = 100ºC), this process is described by the expression

           Q₁ = m₁ c_{e 1} (T_f- T₀)

  • It has a change of state from liquid to gas,

           Q₂ = m₁ L₁

Where L₁ is the latent heat of evaporation, which for water

          L₁ = 2.26 10⁶ J/kg

Consequently the heat absorbed by water is

            Q_{abs} = Q₁ + Q₂

            Q_{abs} = m₁ c_{e 1} (T_f- T₀) + m₁ L₁

Gold is the hottest body and has a process of change of state from the liquid state to the solid state.

           Q_{give } = m₂ L₂

           L₂ = 6.44 10⁴ J / kg

If we assume that there are no losses with the environment

           Q_{abs} = Q_{give}

           m₁ c_{e 1} (T_f- T₀) + m₁ L₁ = m₂ L₂

           m₁ = [tex]\frac{m_2 \ L_2}{ c_{e \1} (T_f - T_o) + L_1 }[/tex]

           m₁ = [tex]\frac{0.140 \ 6.44 \ 10^4 }{4186 (100-23) + 2.26 \ 10^6}[/tex]

           m₁ = 0.9016 104 / 2.592 10⁶

           m₁= 3.48 10⁻³ kg

Using the conservation of energy in calorimetry we can find the amount of water to transform gold from the liquid state to the solid state is

           m = 3.48 10⁻³ kg

Learn more about calorimetry here:

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