El calor derrite el hielo.

Derrite is the third-person singular present tense form of the verb derretir.

So:

• derretir = the infinitive, to melt
• derrite = he/she/it melts

In this sentence, the subject is el calor, so Spanish uses derrite:

• El calor derrite el hielo.

Because derretir is a stem-changing verb in the present tense.

The e in the stem changes to ie in most forms:

• yo derrito
• tú derrites
• él/ella derrite
• nosotros derretimos
• vosotros derretís
• ellos derriten

So derrite is the correct form for el calor.

Because both nouns are masculine singular:

• el calor
• el hielo

Also, Spanish often uses the definite article where English uses no article in general statements.

So English says:

• Heat melts ice

But Spanish commonly says:

• El calor derrite el hielo

Here, el does not necessarily mean the in a very specific sense. It can also help express a general truth.

In this sentence, the usual Spanish word order helps:

• El calor = subject
• derrite = verb
• el hielo = direct object

So the pattern is:

• Subject + verb + object

That means heat is doing the action, and ice is receiving it.

In other words:

• el calor melts
• el hielo gets melted

No. In standard Spanish, h is silent.

So hielo is not pronounced with an English h sound.

It sounds roughly like:

• YE-lo

The beginning hie- is pronounced like ye- in most modern pronunciation.

The rr is pronounced with a strong rolled or trilled r.

So derrite is roughly:

• de-RRI-te

This is stronger than the single r sound in words like caro.

A useful contrast is:

• pero = single r
• perro = double rr

In derrite, you need that stronger rr sound.

Because the subject, el calor, is singular.

Spanish verbs agree with the subject:

• El calor derrite... = singular subject, singular verb
• Las altas temperaturas derriten... = plural subject, plural verb

So derrite matches el calor.

Yes, but it means something slightly different in structure.

• El calor derrite el hielo = Heat melts ice

  • This is transitive: something melts something.

• El hielo se derrite = The ice melts

  • This is pronominal/intransitive: the ice undergoes the change itself.

Both are natural, but they focus on different things:

• El calor derrite el hielo focuses on the cause.
• El hielo se derrite focuses on what happens to the ice.

Because el hielo is a thing, not a person.

Spanish uses the personal a mainly with specific people (and sometimes animals or personified beings):

• Veo a María
• Escucho a mi profesor

But with things, you normally do not use a:

• El calor derrite el hielo

So this sentence correctly has no a.

Yes. Calor is normally a masculine noun:

• el calor

You may occasionally come across poetic or old-fashioned uses with la calor in some regions or styles, but for standard modern Spanish—especially for learners—you should use:

• el calor

No. It is masculine because that is simply its grammatical gender:

• el hielo

Its gender is not caused by the sound at the beginning. You just need to learn it as a masculine noun.

So:

• el hielo frío
• mucho hielo
• este hielo

All of these show that hielo is masculine.

Yes, but El calor derrite el hielo is the most neutral and straightforward order.

Spanish allows some flexibility, but changing the order can change the emphasis. For example:

• El calor derrite el hielo = neutral statement
• El hielo lo derrite el calor = more emphasis on the ice
• Con el calor, el hielo se derrite = emphasis on the condition/cause

For a learner, the original version is the safest and most natural basic pattern.

Yes. It sounds natural as a simple scientific or everyday statement.

Spanish often uses the definite article in general truths:

• El calor derrite el hielo
• El agua hierve a 100 grados
• El frío conserva algunos alimentos

So this sentence works well as a general statement, not just about one specific heat source and one specific piece of ice.