It is ok to have a negative percent error? I got a negative value for the percent error of the enthalpy of the formation of methane gas

Sure. If the experimental value is less than the actual value the percent error is negative. If the experimental value is larger than the actual value the percent error is positive. But most (at least many) people use the absolute value of the error when reporting in which case + or - makes no difference.

No, it is not okay to have a negative percent error. Percent error is a measure of the accuracy of a measurement or calculation, and it is always expressed as a positive value. Negative percent error would imply that the observed or calculated value is smaller than the accepted or expected value, which is not possible.

To calculate percent error, use the following formula:
Percent Error = |(Accepted Value - Observed Value)| / Accepted Value x 100%

If you obtained a negative value for the percent error of the enthalpy of the formation of methane gas, you should double-check your calculations or measurements to identify any mistakes.

Typically, negative percent error is considered acceptable and does have its own meaning. It indicates that the measured value is lower than the expected value. However, it is important to understand the context in which you obtained the negative percent error.

To calculate percent error, you need two values: the experimental or measured value, and the accepted or theoretical value. Percent error is determined using the formula:

Percent error = [(Measured value - Accepted value) / Accepted value] x 100

If you obtained a negative percent error for the enthalpy of formation of methane gas, it means that your measured value is lower than the accepted value. This suggests that there may have been some errors or uncertainties in your experiment that caused the measured value to be lower than expected.

To further analyze the negative percent error, you can consider evaluating the sources of error in your experiment. These can include instrumental limitations, procedural errors, or uncertainties in data collection. By identifying and addressing these sources of error, you can improve the accuracy of your measurements and aim for a smaller or positive percent error in future experiments.

In summary, negative percent error is not inherently wrong or bad, but it suggests that there may have been some issues in the measurement process. It is useful to investigate and understand the reasons behind the negative percent error to improve the accuracy and reliability of experimental measurements.