To determine which units are valid for describing specific heat capacity, we should first understand what specific heat capacity measures. Specific heat capacity is the amount of heat required to change the temperature of a unit mass of a substance by one degree Celsius or one Kelvin.
The key components in the unit of specific heat capacity include:
1. Energy: This can be represented in units such as joules (J) or calories (cal).
2. Mass: This can be represented in units such as grams (g) or kilograms (kg).
3. Temperature change: This can be measured in degrees Celsius (°C) or Kelvin (K).
Now, let's evaluate each given unit:
1. kJ/mol:
- Kilojoules per mole is not a valid unit for specific heat capacity because it involves moles (amount of substance) instead of mass.
2. J/(g K):
- Joules per gram-Kelvin is valid because it describes the energy required to change the temperature of one gram of a substance by one Kelvin.
3. cal/(kg K):
- Calories per kilogram-Kelvin is also valid because it describes the energy required to change the temperature of one kilogram of a substance by one Kelvin.
4. kJ/(mol kg°C):
- Kilojoules per mole-kilogram-degree Celsius is not valid because it includes moles and a combination of mass units, which makes it inconsistent for specific heat capacity.
5. Cal:
- A Calorie (with a capital 'C') is a unit of energy itself and not a measure of specific heat capacity. Thus, it is not valid.
6. J/(g °C):
- Joules per gram-degree Celsius is valid because it describes the energy required to change the temperature of one gram of a substance by one degree Celsius.
7. W/(g °C):
- Watts per gram-degree Celsius is a unit of power per mass and temperature, not specific heat capacity which is energy per mass per temperature change.
In summary, the valid units for specific heat capacity are:
- J/(g K)
- cal/(kg K)
- J/(g °C)
These correspond to items numbered [1, 3, 6].
