Barr's class was the worst class, no the worst experience of my time here at UCLA. The material that this class covers could and should constitute a fairly relaxing class. None of it is overly complicated or difficult in and of itself.
However, Barr somehow manages to make this likely one of the worst classes across every UC. The false confidence that you are given from the extremely simplified and surface level lectures is instantly annihilated by the slaughterhouse that is the first midterm. IF you manage to escape and survive the darkness of this valley, there is no true peak to be found. Just as you start climbing the other side, the floor falls out below you and you plummet into a pit of pure torture, the second midterm. No matter how much you prepare for a midterm with the same difficulty as midterm 1, you will not escape this impending doom. (The average of this midterm was in the low 60s and was not curved).
While this pattern could also somewhat be found in Shao's Chem 20A class, the final provided an oasis at the end of the quarter. Barr did not. The final was the worst test by far. Barr said himself, and I quote, "This one is a doozy." Now, if you are still considering taking this class, note that it is not just the tests which are bad.
To save time I will list the rest of my complaints in bullet point fashion.

-No answers to any practice problems unless you go to every "optional" office hours
-Not even TAs were given all of the solutions
-Office hours by Barr were far too slow and rarely got to difficult concepts
-Some people had to retake this class for scoring too low on the final even though their overall grades were high C's to low B's (would not budge on bumping people 1% up to the bar(pun intended))
-Group homework assigned Friday night and due early Monday morning
-Assignments on about 50 different websites which are very easy to miss
-Somehow make you feel like its all your fault

Don't take this class. I know you have to. But don't. Take it at a community college if you have to.
Only advice I have if you are unfortunate enough to take this class:

-realize GPA isn't that big of a deal
-go to TA office hours

Im sorry

Like many others, I was allured by the veneer of understanding Dr. Barr has. The initial emphasis on mental health and wellbeing was supportive all well and good until tested. His empathy seems to extend quite far in his speech until the actual exam. Besides the convoluted absurdities asked on the exam, and his unwillingness to scale, even in a global pandemic when people are taking the class online in every time zone, for freshman general chemistry! That's not very empathetic. I cannot imagine a general chemistry class being unscaled at a university like UCLA. However, I wanted to give him another chance for the second exam because I was thinking he would listen to student feedback, but as I suspected, absolutely no changes were made in the manner in which the questions were asked. Much of the lectures are filled with superfluous, unnecessary speech which makes chemistry (an already difficult enough subject) all the more complicated. The "systems" of the class are overly complicated and unnecessary. There are two portals for surveys, homework assignments are collaborative without any decision made by the student. It is clear that we are the first round in a new-age type pedagogy and it's not working. The only good thing about this class is the GroupMe, where it is a community of 500 students all bonding over the constant suffering of this class, and collective outrage at many aspects of this course. Do not take this class!!

No matter how much you study, it won't be enough. The midterms are very difficult and all application questions with probably more biology concepts than chemistry. On top of this, Barr is extremely stubborn and does not even take into account the surveys he makes us do. I just do not understand how this is allowed, ESPECIALLY BECAUSE THERE IS NO CURVE! He claims that he is "empathetic" to us because we are in troubling times, but then he troubles the troubling times by giving us exam questions we know nothing about.

Pros:1. The professor seems like a nice person

Cons: 1. The tests are little related to review sessions, homework, and lectures
2. No curve
3. No extra point
4. Feel like chemistry is so scary
5. Really frustrating feeling when taking this class

Advices for people want to take this class: don't put so much time on review sessions because then you would find out that you are "studying for a different exam".

The chem department as a whole just does not care for its students and Professor Barr is just a product of that. He tells us that he can't give 24 hour exams because "his hands are tied" and "it's what the department has mandated". This would be fine if this was true because then he truly couldn't do anything. However, this is all a lie. The Chem Labs give 24 hour exams and I heard that the Chem 20BH get 24 hour exams. He also told us that the first midterm would be easier than the homework. Again another lie. Lying to his students is just one of the many things that I don't like about this class. The other thing I do not like about the class is that in our discussions, the TA's and the LA's try to be as helpful as they can be but what is the point if you aren't going to test us on the things we've been studying. Professor Barr also likes to say that he "empathizes" with our situation. He can say it as many times as he wants but if he does nothing to address the many issues that we students come to him for, then he might as well say nothing at all. He does not accommodate for international students either. Even when you spend the extra time to go to his Office Hours, he barely helps you and instead gives you an answer that just leaves you with more questions. Again Professor Barr is just a product of the Chemistry Department not caring. After someone in the class sent an email to the department begging to understand the reason for all of this, the department implied that Barr is a great professor and very qualified. Ahem I don't know if being very smart makes you qualified to teach but I guess I wouldn't know since I'm a student. But I guess the department wouldn't know either since they can sit at the top and act so aloof. You can't ask a principal to understand the struggles in a classroom because they never sit in there day in day out so how would you expect the "prestigious" Chemistry Department of UCLA to understand the struggles of a student in a global pandemic mind you. I hope that Professor Barr does at least try to learn from all this because there is hope, but the way he is right now... avoid him.

This man needs to be fired. please.

WORST CLASS EVAAAAAAA!!! There was more focus on encouragement than teaching chemistry. He wasn't tolerant and didn't care about anyone's personal issues, such as getting covid. He made it way more difficult to learn than it had to be by never giving answers and sometimes gatekeeping information in his lectures. The class was always treated like elementary students. He actively tried to hide answers and "encourage collaboration" where it wasn't helpful. He used multiple different websites and apps throughout the course making it difficult to keep up with the work. Barr would barely answer specific questions on material and proceed to put that same material on exams. He makes the most complicated test questions about random real life products/events which are difficult to answer with the little teaching he gives on those certain topics. His borderline creepy obsession with Disney has also ruined any good experiences I ever had or will have with that company. I never want to take a chemistry class again and especially not with a teacher that talks about helping his students so much when he is actually inhibiting our learning with the ways he hides information and answers from us. I never want to see anything related to buffers, acids, or bases again out of fear for the PTSD it will bring from this horrendous class. This man's purpose of making the class more difficult than it should be seems to be overshadowing his passion of teaching and ruins any chances of easily learning. His tests progressively got harder while switching from online to in-person which became really difficult with less notes allowed in person and more challenging material. Never taking a class from him again and god forbid anyone else has to either. FUCKIN WEIRDOOOOO!

Some flavor of PTSD

Chances are you arent going to get a choice on this class, so here are some tips:
Find someone to struggle with, go to office hours (TA ones are more useful for answering specific questions, Barr's office hours tend to run through whole problem sets or past midterms), take 20BH if youre relatively confident in chem (obvs didnt take it but have been told its the same workload but tests arent cringe, and hard work in = results out, which is not always the case in this class)
The only way to describe this class is a sisyphean struggle. As soon as you think you've done enough work to get a grasp of the material, the topic changes or Barr throws a problem that feels like a complete departure from every example youve ever done. I feel pretty confident in chemistry and I put a lot of time into this class and it was still a complete struggle on a lot of levels. I tried to like Barr, he gives off the impression that he really cares about how well you do, and then acts in a way that completely contradicts that. He claims that problems sets will help by making you collaborate, but then throw in questions that no one can solve confidently. Midterms are supposed to be on a level with discussion quesions and problem sets - maybe midterm 1 was, midterm 2 had questions that I *dont even know what I'd google if I wanted to solve it* (trust me I tried). Lectures are simultaneously necessary and a waste of time. They dwell for far too long on specific examples while expecting you to extrapolate that to harder and different problems. But don't think you can skip and rely on the textbook or I can assure you, you will be lost - textbook questions do not correlate in any way to questions in this class outside of low level conceptual questions. Barr repeatedly tries to "dress up" questions in "relevant" and "interesting" ways, e.g. using Covid vaccines or amino acids instead of regular acids and bases. The problem is that HE GETS IT WRONG and unless you just assume it acts in a way that youre used to (absolutely no reason why it should) THERE IS NO WAY TO SOLVE THE QUESTION WITH THE INFO WE HAVE.
Khan academy is your friend, Chem LibreTexts is your friend. Be fully prepared to teach yourself almost all the content. There are no words for how bad Barr is, the fact that hes been teaching for only a few years and *every* engineering student hates him. The silver lining on this terrible class is that the content itself is not intrinsically difficult except acids and bases, so its definitely possible to score well if you can navigate the bullshit.

The group you get in is probably the most important thing. I tried to change my group at the start of the quarter but thanks to the TA that did not happen. Then, I had to do all 4 homework by myself for the whole quarter. Barr's a nice dude but you'll hate him for the way he designs his 20B class.