Short Answer 
The thermal energy required to boil a substance is calculated using the formula Q = m λv, where m is the mass and λv is the latent heat of vaporization. For 1.75 kg of water, using a specific latent heat of approximately 3.34 x 10^6 J/kg, the total energy required to completely boil the water is 5,845,000 J.
Step 1: Understand the Formula
The formula to calculate the thermal energy required to boil a substance is Q = m λv, where:
- Q is the total energy (in joules).
- m is the mass of the liquid (in kilograms).
- λv is the specific latent heat of vaporization (in J/kg).
This formula helps us determine the amount of energy needed when heating water to its boiling point and turning it into vapor.
Step 2: Identify Parameters
Next, identify the specific values needed for the calculation:
- Mass of Water (m): In this case, it’s 1.75 kg.
- Specific Latent Heat (λv): For water, it is approximately 3.34 x 106 J/kg.
- Boiling Temperature: We are assuming the water is already at its boiling temperature.
These values are essential to compute the energy required to completely boil the water.
Step 3: Calculate the Energy Required
Utilize the values from the previous step to calculate the energy:
- Plug in the values: Q = (1.75 kg) x (3.34 x 106 J/kg).
- Perform the multiplication to find Q: Q = 5,845,000 J.
- This result means that to completely boil off 1.75 kg of water, you need 5,845,000 J of thermal energy.
Now you have the total amount of energy necessary to boil the water completely.