Critiquing a Classmate’s Post

I am going to constructively criticize one of my classmate’s post. The post is called Physical and Chemical Changes. This is the post :

There is a difference between a physical and chemical change. A physical change is a change that does not result in a new substance like a broken vase. A chemical change is a change that results in one or more new substances like burning wood.


image credit:http://www.flickr.com/search/?q=broken+vase&l=cc&ct=0&mt=all&adv=1

http://www.flickr.com/search/?q=burning+wood&l=cc&ct=0&mt=all&adv=1

I think this post is good because it is an accurate description of Physical and Chemical Changes. However, it is a little too short to be a real summary or paragraph. It is also good that the author used an image along with image credits. I found no spelling mistakes and no grammar mistakes, but one punctuation mistake : The author should’ve put a comma after the word “substance”, both times. The author seems to be an expert at science, and I would show this post to people who need to know about Physical and Chemical Changes, and who also don’t want to read a long essay.