La profesora escribió una palabra con la tiza azul en la pizarra.

Escribió is the preterite, which is used for a completed action in the past.

So La profesora escribió una palabra... means the teacher wrote a word as a finished event.

If you said escribía, that would be the imperfect, which usually suggests:

• an ongoing action in the past,
• a repeated habit,
• or background description.

Compare:

• La profesora escribió una palabra. = The teacher wrote a word.
• La profesora escribía palabras. = The teacher was writing words / used to write words.

In this sentence, the action is presented as one completed event, so escribió is the natural choice.

In Spanish, it is very common to use the definite article with professions or roles when talking about a specific person:

• La profesora = the teacher
• El médico = the doctor
• La estudiante = the student

If you just say profesora by itself, it usually would not work here as a normal subject. Spanish generally wants an article or some other determiner:

• La profesora
• Mi profesora
• Esa profesora

So La profesora escribió... is the normal way to say The teacher wrote...

Una palabra means a word, so it introduces something non-specific or not previously identified.

• una palabra = a word
• la palabra = the word

So:

• La profesora escribió una palabra = The teacher wrote a word.
• La profesora escribió la palabra = The teacher wrote the word.

If the listener already knows which word is meant, la palabra would make sense. If it is just any one word, una palabra is correct.

Because palabra is grammatically a feminine noun in Spanish, so it takes:

• una palabra
• la palabra

This does not mean the object itself is “female.” Grammatical gender is just a noun class.

A useful tip: many nouns ending in -a are feminine, and palabra follows that common pattern.

Here con means with, and it introduces the instrument used to do the action.

So:

• escribió con la tiza azul = wrote with the blue chalk

This is very common in Spanish:

• cortar con un cuchillo = to cut with a knife
• escribir con un bolígrafo = to write with a pen
• pintar con un pincel = to paint with a brush

So con la tiza azul tells you what the teacher used to write.

The most natural reading is she used the blue chalk.

That is because:

• tiza = chalk
• azul is directly describing tiza

So the phrase most straightforwardly means with the blue chalk.

In practice, that often also implies the writing was blue, but grammatically the adjective is attached to tiza, not directly to palabra.

If you wanted to make the colour of the writing especially clear, Spanish might use something like:

• escribió una palabra en azul en la pizarra = she wrote a word in blue on the board

So this sentence focuses first on the instrument.

In Spanish, adjectives usually come after the noun.

So:

• tiza azul = blue chalk
• coche rojo = red car
• casa grande = big house

That is the normal pattern. English usually puts adjectives before the noun, but Spanish usually puts them after.

Not all Spanish adjectives change form for gender.

Azul is one of many adjectives that have the same form for masculine and feminine singular:

• el coche azul
• la tiza azul

It only changes in the plural:

• los coches azules
• las tizas azules

So azul is correct with both masculine and feminine singular nouns.

En usually means in or on, depending on context.

With pizarra, it means on the board:

• escribió en la pizarra = wrote on the board

Spanish uses en for this kind of location:

• en la mesa = on the table
• en la pared = on the wall
• en el papel = on the paper

So even though English says on the blackboard, Spanish uses en la pizarra.

In Spain, pizarra commonly means a board used for writing in class.

Traditionally, it means a blackboard/chalkboard, but it can also be used more generally depending on context. If someone wants to be very specific about a whiteboard, they might say:

• pizarra blanca = whiteboard

In this sentence, because it also mentions tiza (chalk), the image is very naturally a chalkboard/blackboard.

The basic sentence is perfectly natural as it stands, but Spanish word order is often more flexible than English.

This sentence can be rearranged, especially with the prepositional phrases:

• La profesora escribió una palabra en la pizarra con la tiza azul.
• En la pizarra, la profesora escribió una palabra con la tiza azul.

These all mean roughly the same thing, though the emphasis changes slightly.

The original order is clear and neutral:

• subject: La profesora
• verb: escribió
• direct object: una palabra
• instrument: con la tiza azul
• location: en la pizarra

Because una palabra is a direct object that is a thing, not a specific person.

Spanish uses the personal a before many human direct objects:

• Veo a la profesora. = I see the teacher.
• Conozco a María. = I know María.

But with things, you usually do not use that a:

• Escribió una palabra.
• Compré un libro.
• Vi una mesa.

So una palabra appears without a.

Not normally in this sentence.

Spanish usually uses articles where English sometimes does not:

• con la tiza azul
• en la pizarra

If you said con tiza, that could sound more like with chalk in a general material sense, not necessarily with the blue chalk as a specific object.

And en pizarra would not sound natural here. You need en la pizarra.

So the articles help make the sentence sound complete and idiomatic.

Yes, tiza is a feminine noun:

• la tiza
• una tiza

So in this sentence:

• con la tiza azul

That matches the noun’s grammatical gender.

A little, yes, but not in a serious way.

The main possible question is whether azul is describing:

• the chalk, or
• the colour of the written word

Grammatically, it most directly describes tiza, so the default reading is:

• with the blue chalk

But because blue chalk writes in blue, the real-world meaning overlaps.

If a speaker wanted to avoid even slight ambiguity, they could say:

• La profesora escribió una palabra con la tiza azul en la pizarra.
  very natural, instrument-focused
• La profesora escribió una palabra en azul en la pizarra.
  colour-of-writing-focused

So the original sentence is normal and understandable, but Spanish can be more specific if needed.