## Thallium – Specific Heat, Latent Heat of Fusion, Latent Heat of Vaporization

**Specific heat of Thallium is ****0.13 J/g K**.

**Latent Heat of Fusion of Thallium is ****4.142 kJ/mol**.

**Latent Heat of Vaporization of Thallium is ****164.1 kJ/mol**.

**Specific Heat**

**Specific heat, or specific heat capacity, **is a property related to** internal energy** that is very important in thermodynamics. The **intensive properties c_{v}** and

**are defined for pure, simple compressible substances as partial derivatives of the**

*c*_{p}**internal energy**and

*u(T, v)***enthalpy**, respectively:

*h(T, p)*where the subscripts **v** and **p** denote the variables held fixed during differentiation. The properties **c _{v} **and

**c**are referred to as

_{p}**specific heats**(or

**heat capacities**) because under certain special conditions they relate the temperature change of a system to the amount of energy added by heat transfer. Their SI units are

**J/kg K**or

**J/mol K**.

**Different substances **are affected to **different magnitudes **by the **addition of heat**. When a given amount of heat is added to different substances, their temperatures increase by different amounts.

**Heat capacity** is an extensive property of matter, meaning it is proportional to the size of the system. **Heat capacity C** has the unit of energy per degree or energy per kelvin. When expressing the same phenomenon as an intensive property, the **heat capacity** is divided by the amount of substance, mass, or volume, thus the quantity is independent of the size or extent of the sample.

**Latent Heat of Vaporization**

In general, when a material **changes phase** from solid to liquid, or from liquid to gas a certain amount of energy is involved in this change of phase. In case of liquid to gas phase change, this amount of energy is known as the **enthalpy of vaporization**, (symbol ∆H_{vap}; unit: J) also known as the **(latent) heat of vaporization** or heat of evaporation. As an example, see the figure, which descibes phase transitions of water.

Latent heat is the amount of heat added to or removed from a substance to produce a change in phase. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas (the **pΔV work**). When latent heat is added, no temperature change occurs. The enthalpy of vaporization is a function of the pressure at which that transformation takes place.

**Latent Heat of Fusion**

In case of solid to liquid phase change, the change in enthalpy required to change its state is known as the enthalpy of fusion, (symbol ∆H_{fus}; unit: J) also known as the **(latent) heat of fusion**. Latent heat is the amount of heat added to or removed from a substance to produce a change in phase. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the system (the **pΔV work**).

The liquid phase has a higher internal energy than the solid phase. This means energy must be supplied to a solid in order to melt it and energy is released from a liquid when it freezes, because the molecules in the liquid experience weaker intermolecular forces and so have a higher potential energy (a kind of bond-dissociation energy for intermolecular forces).

The temperature at which the phase transition occurs is the **melting point**.

When latent heat is added, no temperature change occurs. The enthalpy of fusion is a function of the pressure at which that transformation takes place. By convention, the pressure is assumed to be 1 atm (101.325 kPa) unless otherwise specified.

## Thallium – Properties

Element | Thallium |
---|---|

Atomic Number | 81 |

Symbol | Tl |

Element Category | Poor Metal |

Phase at STP | Solid |

Atomic Mass [amu] | 204.3833 |

Density at STP [g/cm3] | 11.85 |

Electron Configuration | [Hg] 6p1 |

Possible Oxidation States | +1,3 |

Electron Affinity [kJ/mol] | 19.2 |

Electronegativity [Pauling scale] | 1.62 |

1st Ionization Energy [eV] | 6.1083 |

Year of Discovery | 1861 |

Discoverer | Crookes, William |

Thermal properties | |

Melting Point [Celsius scale] | 303 |

Boiling Point [Celsius scale] | 1457 |

Thermal Conductivity [W/m K] | 46 |

Specific Heat [J/g K] | 0.13 |

Heat of Fusion [kJ/mol] | 4.142 |

Heat of Vaporization [kJ/mol] | 164.1 |

## Thallium in Periodic Table

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