def convert_energy_unit(energy_val, current_unit, new_unit):
    """
    Convert `energy_val` from the `current_unit` to `new_unit`.
    Only support kJ/mol, kcal/mol, and J/mol.
    """
    if current_unit == 'kJ/mol' and new_unit == 'kcal/mol':
        return energy_val / 4.184
    elif current_unit == 'kJ/mol' and new_unit == 'J/mol':
        return energy_val * 1000
    elif current_unit == 'J/mol' and new_unit == 'kJ/mol':
        return energy_val / 1000
    elif current_unit == 'J/mol' and new_unit == 'kcal/mol':
        return energy_val / 4184
    elif current_unit == 'kcal/mol' and new_unit == 'kJ/mol':
        return energy_val * 4.184
    elif current_unit == 'kcal/mol' and new_unit == 'J/mol':
        return energy_val * 4184
    else:
        raise ValueError("Unsupported units")