Tengo que cambiar el cordón de mis zapatillas porque se rompió.

Tener que + infinitive is one of the most common ways to express obligation in Spanish.

• tengo = I have
• que = part of the fixed structure
• cambiar = to change

So tengo que cambiar literally looks like I have that to change, but in natural English it means I have to change.

Other forms:

• tienes que = you have to
• tenemos que = we have to
• tuvieron que = they had to

After tener que, Spanish uses the infinitive form of the verb.

So:

• tengo que cambiar = I have to change
• not tengo que cambio

That is the same pattern as:

• quiero comer = I want to eat
• voy a salir = I’m going to go out
• puedo ayudarte = I can help you

When one verb follows another structure like this, the second verb is very often in the infinitive.

Here cordón means shoelace.

More broadly, cordón can also mean:

• a cord
• a lace
• a drawstring

In this sentence, because of mis zapatillas, the meaning is clearly shoelace.

In everyday Spanish, especially when talking about shoes, you will also often hear the plural:

• los cordones = shoelaces

Because the speaker is talking about one lace, not both.

So:

• el cordón de mis zapatillas = the lace of my trainers / one of my shoelaces

If you wanted to talk about both laces, you would normally say:

• los cordones de mis zapatillas = the shoelaces of my trainers

The sentence suggests that just one lace broke, so only one needs replacing.

In Spain, zapatillas usually means trainers / sneakers.

This is important because vocabulary varies across the Spanish-speaking world. In other places, people might say:

• tenis
• zapatillas deportivas
• zapatos deportivos

But in Spain, zapatillas is very normal for casual sports shoes or sneakers.

Spanish usually shows possession with de, not with an apostrophe structure like English.

So:

• el cordón de mis zapatillas = literally the lace of my trainers

This is the normal Spanish way to say:

• my trainers’ lace
• or more naturally in English, the shoelace of my trainers

Spanish often prefers:

• el libro de Ana = Ana’s book
• la puerta del coche = the car door
• el color de la camisa = the colour of the shirt

Not in this exact sentence, because the sentence is talking about one lace.

You could say:

• Tengo que cambiar uno de los cordones de mis zapatillas porque se rompió. = I have to replace one of the shoelaces of my trainers because it broke.

Or if both were damaged:

• Tengo que cambiar los cordones de mis zapatillas porque se rompieron. = I have to replace the shoelaces of my trainers because they broke.

So the singular or plural depends on what actually broke.

Because porque here means because.

This is a very common confusion:

• porque = because
• por qué = why
• porqué = the reason
• porque can also occasionally appear in other structures, but because is the key meaning here

Examples:

• No fui porque estaba cansado. = I didn’t go because I was tired.
• ¿Por qué no fuiste? = Why didn’t you go?

In your sentence, it gives the reason:

• porque se rompió = because it broke

Because romperse is very commonly used to mean to break in the sense of become broken.

So:

• romper = to break something
• romperse = to break / to get broken / to become broken

Compare:

• Rompí el vaso. = I broke the glass.
  Here, someone caused the action.
• El vaso se rompió. = The glass broke.
  Here, the glass became broken.

In your sentence:

• el cordón se rompió = the lace broke

The se does not mean itself in a literal English sense here. It is part of a very common Spanish way to express that something broke, opened, closed, melted, etc.

The preterite is used because the breaking is seen as a completed event.

• se rompió = it broke
• a single finished action in the past

That fits the context well: at some point, the lace broke, and now the speaker needs to replace it.

If you used the present perfect in Spain, you might also hear:

• porque se ha roto

In Spain, that can sound very natural if the break feels recent or relevant to the present. Both are possible depending on context.

Yes, but cambiar is the more everyday, natural verb here.

• cambiar el cordón = change / replace the lace
• reemplazar el cordón = replace the lace

Reemplazar is correct, but it can sound a little more formal or less conversational in some contexts. For ordinary daily speech, cambiar is often the most natural choice.

Spanish often uses the definite article where English might sometimes omit it.

So:

• el cordón = the lace

Even though English might say I need to replace a shoelace or my shoelace, Spanish commonly says el cordón and then adds more information:

• el cordón de mis zapatillas

This is a very normal Spanish structure.

In this context, cambiar means replace, not just change in a vague sense.

Because the reason is:

• porque se rompió = because it broke

So the meaning is clearly:

• I have to replace the shoelace of my trainers because it broke

If the lace were only loose, dirty, or badly tied, the meaning would be different.

Yes. Some natural alternatives are:

• Tengo que cambiar el cordón de mis zapatillas porque se ha roto.
• Tengo que cambiar uno de los cordones de mis zapatillas porque se rompió.
• Se me ha roto el cordón de las zapatillas, así que tengo que cambiarlo.

All of these are natural. The original sentence is understandable and correct, but in real conversation, a speaker might choose a version that makes it even clearer that only one lace broke.

Mis means my and agrees with the plural noun zapatillas.

Compare:

• mi zapatilla = my trainer / my sneaker
• mis zapatillas = my trainers / my sneakers

Even though English often treats a pair of sneakers as one item, Spanish usually talks about the two shoes in the plural:

• mis zapatillas
• mis zapatos
• mis botas

So mis is plural because zapatillas is plural.