Translation:It is hard to finish that work in one day.
You're right, I was not clear enough.
Your sentence is correct if you add a comma after "faire", then "ce travail" is stressed, but still subject of "est": "il (=ce travail) est difficile à faire, ce travail"
Now if you use the impersonal formula "il est difficile de...", "il" is not replacing travail, since the end of the sentence has to be "... faire ce travail" ("travail" is object of "faire")
Guidelines for choosing à or de in the following construct:
adjective / noun + preposition + infinitive
Consider the following English sentence : It is difficult to eat.
This sentence is ambiguous since it could have a number of meanings, such as:
• the act of eating is difficult (because I have a sore throat)
• the lobster that I am eating is difficult to eat
In French this ambiguity is removed by using de and à.
Generally, when the subject is a dummy subject you need the preposition de and when the subject is concrete you need the preposition à
Il est important d'étudier. - It is important to study (the word it acts as a dummy subject)
il est bon d'exercer - it is good to exercise (the word it acts as a dummy subject)
Il est difficile de manger parce que j'ai mal à la gorge - it is difficult to eat because I have a sore throat
le homard est difficile à manger - the lobster is difficult to eat
votre essai était difficle à lire - your essay was difficult to read
Also note that you use the structure adjective / noun + de + infinitive for something that conveys an abstract concept. Abstract nouns refer to intangible things, like emotions, feelings, ideals, concepts and qualities. Nouns like freedom, justice, love, beauty are abstract nouns.
Elle est prête à partir - She is ready to leave
Je suis triste de partir. - I am sad to leave (sadness is an abstract concept) chacun est libre de choisir - everyone is free to choose
vous êtes libre de partir - you are free to leave
When "ce" is followed by a noun, it is a demonstrative adjective, masculine and singular.
The French demonstrative adjectives are:
- ce chien = masculine singular, before a word starting with a consonant sound = this/that dog
- cet homme / cet arbre = masculine singular, before a word starting with a vowel sound = this/that man / tree
- cette femme / cette eau = feminine singular = this/that woman / water
- ces chiens / ces hommes / ces arbres, / ces femmes / ces eaux = all plural forms.
In proper French and definitely in writing, the impersonal construction is "il est + adjective + de/que", and not "c'est + adj + de/que".
The grammatical reason is that ce/c' is a real subject (this/that) and not an impersonal pronoun (like "il/it").
For example, "il est facile de mentir" (it is easy to lie) is correct, but "c'est facile de mentir" (this is easy to lie) would have 2 subjects: What is easy? "c'" and "de mentir.
In spoken French, the improper construction with "c'est" is however massively used, but since we have to teach you proper French, we are trying to apply the rules.