На первой лекции учительница по истории говорила чётким спокойным голосом.

Both на and в can mean “at / in”, but Russian uses them with different types of events and places.

For lessons, lectures, concerts, meetings, etc., you normally say:

• на лекции – at the lecture
• на уроке – in class
• на концерте – at the concert

Using в лекции would sound wrong in this context, because a lecture is treated as an event, not as a physical container you’re “inside.” So:

• на первой лекции = at the first lecture (correct, natural)
• в первой лекции – sounds ungrammatical here.

In Russian, the preposition на requires the prepositional case here.

• Nominative: первая лекция – the first lecture (as a subject)
• Prepositional: на первой лекции – at the first lecture

The adjective первой must match лекции in:

• gender (feminine),
• number (singular),
• case (prepositional).

So you cannot keep the adjective in nominative (первая) if the noun is in the prepositional (лекции). They have to agree: на первой лекции.

The form лекции can indeed be:

• singular: genitive / dative / prepositional of лекция
• plural: nominative / accusative of лекции

Here context and the adjective make it clear:

• первой лекции – “first lecture” can only be singular, because:
  • первой is the feminine, singular, prepositional form of первая;
  • you don’t usually say “at the first lectures.”

If it were plural, you’d expect something like:

• на первых лекциях – at the first lectures (prepositional plural).

So на первой лекции is clearly singular: at the first lecture.

Учительница по истории literally is “female teacher of history,” i.e. history teacher (female).

• Preposition по here means something like “of / in the subject of”.
• After по, school subjects are put in the dative case, and for история (fem. noun) the dative singular is истории.

So grammatically:

• учительница – nominative, feminine, singular (subject)
• по истории – по
  • dative singular, indicating the subject she teaches

The pattern is common:

• учитель по математике – math teacher
• учительница по русскому языку – Russian language teacher

Both refer to a history teacher, but with some nuances:

1. учительница по истории

   • Emphasizes that the teacher is female (-ница is a feminine suffix).
   • по истории is the “subject” construction (teacher of the subject history).
   • Sounds more typical in everyday school context: our (female) history teacher at school.

2. учитель истории

   • Grammatical gender is not explicit; default is masculine unless context says otherwise.
   • истории here is genitive, literally teacher of history.
   • Slightly more neutral/formal, often used in writing, CVs, etc.

You could say:

• Моя учительница по истории очень строга. – My (female) history teacher is very strict.
• Он учитель истории. – He is a history teacher.

Говорила and сказала both relate to “speaking,” but differ in aspect and meaning:

• говорила – past tense, imperfective, from говорить

  • Emphasizes the process, how she spoke over a period of time.
  • Fits well with чётким спокойным голосом (clear, calm voice), describing the manner.

• сказала – past tense, perfective, from сказать

  • Emphasizes a single finished act of saying something.
  • Typically used for a specific statement or result: she said X.

The sentence focuses on how she was speaking during the lecture, not on a particular phrase she uttered, so говорила is the natural choice.

Голосом is the instrumental singular of голос (voice).

Russian uses the instrumental case to express means or manner – by means of what / how something is done.

• говорила голосом = “(she) spoke with a voice”
• Adding adjectives: чётким спокойным голосом = “with a clear, calm voice” / “in a clear, calm voice.”

This is a very common pattern:

• говорить тихим голосом – to speak in a quiet voice
• говорить уверенным голосом – to speak in a confident voice

So говорила чётким спокойным голосом literally is “she spoke with a clear, calm voice,” describing manner of speaking.

The adjectives must agree with голосом (instrumental, masculine, singular):

• голосом (instr. masc. sg.)
• чётким, спокойным (instr. masc. sg. forms)

So both are in the instrumental case because they describe голосом.

About the endings:

• чёткий → чётким
• спокойный → спокойным

The difference -им vs -ым is mostly spelling/phonetics, not grammar:

• After К, Г, Х, Ж, Ч, Ш, Щ you usually write И, not Ы, in endings.
• The stem of чёткий ends in к (чётк-), so you must write -им: чётким.
• спокойный has a stem ending in н, so the normal -ым ending is used: спокойным.

Both are instrumental masculine singular forms; the difference is just the standard spelling rule.

Here чётким спокойным голосом is just a simple series of two adjectives before a noun. In Russian:

• No comma is used between two ordinary adjectives before a noun:
  • чётким спокойным голосом
  • маленький красный мяч – a small red ball

You can add и:

• чётким и спокойным голосом

This is also correct and emphasizes them as two separate qualities slightly more explicitly, like “a clear and calm voice.” Without и, they form a more compact descriptive group.

Yes. Russian word order is relatively flexible, and several variants are possible and natural:

• На первой лекции учительница по истории говорила чётким спокойным голосом.
• Учительница по истории на первой лекции говорила чётким спокойным голосом.
• Учительница по истории говорила на первой лекции чётким спокойным голосом.

All are grammatically correct. The differences are in focus / emphasis:

• Starting with На первой лекции highlights the time/situation: “At the first lecture, the history teacher…”
• Starting with Учительница по истории highlights who is acting: “The history teacher, in the first lecture, spoke…”

For a learner, the original word order is perfectly normal and neutral.

In Russian, verbs in the past tense must agree with the gender of the subject.

• учительница – grammatically feminine
  
  • → говорила (past feminine)
• учитель – grammatically masculine
  
  • → говорил (past masculine)

So:

• Учительница по истории говорила чётким спокойным голосом.
• Учитель по истории говорил чётким спокойным голосом.

Even if in English you just say “teacher,” in Russian you must show gender in the past tense verb.

You can say:

• Во время первой лекции учительница по истории говорила чётким спокойным голосом.

This is grammatically correct, but the nuance changes slightly:

• на первой лекции – at / during the first lecture in a general, natural way for events.
• во время первой лекции – during the time of the first lecture, a bit more explicitly temporal and sometimes slightly more formal or “written.”

In most everyday contexts describing classroom situations, на первой лекции sounds more idiomatic and neutral.