Мы обсуждаем роман известного писателя в чате.

Because обсуждать takes a direct object, and direct objects are usually in the accusative case.

Here, роман is a masculine inanimate noun. For masculine inanimate nouns, the accusative singular is the same as the nominative singular, so:

• nominative: роман
• accusative: роман

So the form does change grammatically, but it just happens to look identical.

Because it means something like the novel of a famous writer or a novel by a famous writer.

The noun писатель depends on роман and shows relationship/possession, so Russian uses the genitive case:

• писатель → писателя

The adjective must agree with the noun it describes, so:

• известный писатель
• известного писателя

Both words are masculine singular genitive.

В чате is in the prepositional case.

After в, Russian usually uses:

• prepositional for location: in / at
• accusative for motion into somewhere

So:

• в чате = in the chat
• compare: в чат = into the chat

Since the sentence describes where the discussion is happening, not movement, prepositional is used.

Обсуждаем means:

• present tense
• 1st person plural
• from the infinitive обсуждать

So it means we discuss or we are discussing.

Russian present tense often covers both the simple present and the present continuous meanings that English separates.

Because the sentence presents the action as an ongoing process: we are discussing.

Обсуждать is the imperfective verb, which is used for:

• ongoing actions
• repeated actions
• general process

Its perfective partner is обсудить, which focuses on completion. For example:

• Мы обсуждаем роман = we are discussing the novel
• Мы обсудим роман = we will discuss the novel / discuss it through to completion

Yes, very often.

Russian often drops subject pronouns when the verb ending already makes the subject clear. The ending -ем in обсуждаем already tells you it is we.

So both are possible:

• Мы обсуждаем роман известного писателя в чате.
• Обсуждаем роман известного писателя в чате.

Including мы can add emphasis, contrast, or clarity.

Russian word order is fairly flexible because the cases show what each word is doing.

The given order is neutral and natural:

• Мы обсуждаем роман известного писателя в чате.

You can move parts around for emphasis, for example:

• В чате мы обсуждаем роман известного писателя.
  This emphasizes where the discussion happens.

• Роман известного писателя мы обсуждаем в чате.
  This emphasizes what we are discussing.

So word order in Russian often affects focus and style, not just grammar.

No. Роман can also mean romance or love affair in some contexts.

But in this sentence, роман известного писателя clearly means a novel by a famous writer, because писатель strongly points to literature.

So this is a good example of how context decides the meaning.

Because adjectives in Russian must agree with the noun they describe in:

• gender
• number
• case

Here, писателя is:

• masculine
• singular
• genitive

So the adjective must also be masculine singular genitive:

• известный → известного

This -ого ending is a standard genitive ending for many masculine and neuter adjectives.

Russian usually does not have words corresponding directly to English a and the.

That means the sentence can be interpreted from context as something like:

• We are discussing a novel by a famous writer in the chat
• We are discussing the novel of a famous writer in the chat

Context usually makes the intended meaning clear. If Russian speakers want to be more specific, they may use words like этот for this or change the wording.

Yes. In modern Russian, чат usually means a chat, especially an online or messaging chat.

So в чате naturally means:

• in the chat
• in the group chat
• in the messaging thread

The exact type depends on context, but the phrase sounds very natural in modern everyday Russian.