The amount of heat required to turn water into steam depends on several factors, including the initial temperature and pressure of the water. However, the specific heat of water and the heat of vaporization are typically used to estimate the energy required.
To convert water at its boiling point (100 degrees Celsius at sea level) into steam at the same temperature, it takes approximately 540 calories (or 2,260 joules) of heat per gram of water. This energy is known as the heat of vaporization. This value is relatively high compared to other substances due to the strong hydrogen bonding between water molecules.
Now, let's address your second question. While Earth's core is indeed very hot, with temperatures estimated to be around 5,500 to 6,000 degrees Celsius, the surface temperature is significantly lower. The surface temperature varies across different regions, but it typically ranges from -90 degrees Celsius in Antarctica to around 50 degrees Celsius in some desert areas.
The reason the entire planet doesn't become one giant steam engine is primarily due to the following factors:
Heat transfer: The heat from the core is transferred to the Earth's surface through conduction and convection. However, the process of heat transfer is relatively slow over large distances and encounters various barriers, such as the solid mantle and crust.
High pressures: At the Earth's core, the pressure is incredibly high, estimated to be around 3.6 million times atmospheric pressure. These high pressures keep the water within the Earth's interior in a dense and liquid state, even at extremely high temperatures.
Limited contact with water: Water is not uniformly present throughout the Earth's interior. While there are vast underground water sources, they are not in direct contact with the core, and the heat transfer between them is limited.
In summary, while the Earth's core is indeed extremely hot, the heat transfer mechanisms, high pressures, and limited contact with water prevent the entire planet from becoming a giant steam engine. The complex dynamics of the Earth's interior and the heat dissipation processes help maintain a stable environment on the planet's surface.