Apple vs Samsung: Why this trial will be harder for Apple

Park Ji-Hwan | AFP | Getty Images

The last time Apple and Samsung met in court over mobile patents, the company that brought us the iPhone won significant damages from its rival.

Now the two are back in court, fighting over software patents, and the case doesn't look as promising for Apple this time, a legal expert says.

Read More Apple's damages expert makes case for why company is due $2.19 billion from Samsung

"It's hard to know until you see all the relevant pieces, but an initial read of the patents suggests to me that some of them are written at a very broad level," said Mark McKenna, a law professor at Notre Dame. "It would surprise me if they were upheld at that level of generality."

Apple is making some broad claims about what it owns and will have to make a strong case to prove it actually deserves as much as it is asking for, McKenna said.

In the 2012 patent trial Apple won about $1 billion (it was seeking $2.75 billion) in damages from Samsung for infringing its patents, but did not get an injunction against Samsung devices.

This time, Apple is going after about $2 billion in damages, claiming that Samsung copied five of its patents, and is also seeking a sales ban of several Samsung phones, including its Galaxy S III. Samsung is also accusing Apple of infringing two of its patents and is asking for $7 million.

One reason Apple may have a hard time winning as much cash this time is because four of the five patents the company is claiming Samsung infringed upon are related to features in the handsets' software, which is powered by Google's Android operating system.

Read More Apple's war on Samsung has Google in crossfire

"There was a lot about the last case that had this flavor of 'We were here first and you just knocked off our product,'" Mckenna said. "But you can't do that with software. You can't just wave around code, it's difficult to do with a jury."

And as for an injunction against Samsung devices, that looks less promising than winning its $2 billion claim.

"It seems very unlikely that they will get an injunction," McKenna said. "My sense is if they had a hard time last time asking for this, it would be very hard for them to get it this time."

Read MoreApple again seeks decisive US court ruling against Samsung

But just because it's an uphill battle doesn't mean Apple doesn't have a shot--and if it did win, the impact has the potential to be significant.

"If Apple were to prevail it could dictate some redesign in the Android platform. Not that that is a big deal, there are certainly ways to do it, but it could change the familiarity of Android for users," said Van Baker, an analyst at Gartner.

Apple isn't going directly after Google because the search giant gives the Android software away for free, so there isn't any monetary damages to claim. Instead, Apple is going after Samsung because that is where the profits are and if it wins it forces Google to make some changes.

"If Apple prevails against Samsung that impacts Android overall," Baker said. "It affects every smartphone with Android in the world."

By CNBC's Cadie Thompson.