Is hearing gossip a mortal sin?
Answer: Unless the matter under discussion is a common news item, when someone's gossip negatively alters the opinion another has regarding a third person, one has committed a grave action. If it is done with full knowledge and deliberate consent, the grave action then becomes a mortal sin.
Three conditions must together be met for a sin to be mortal: "Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent." The sin against the Holy Ghost and the sins that cry to Heaven for vengeance are considered especially serious.
1), pertains to detraction, is an act of virtue, either (a) an act of charity, as when someone denounces his brother's sin while intending his improvement, or (b) an act of justice, as when someone accuses his brother. Therefore, detraction is not a mortal sin.
A mortal sin is defined as a grave action that is committed in full knowledge of its gravity and with the full consent of the sinner's will. Such a sin cuts the sinner off from God's sanctifying grace until it is repented, usually in confession with a priest.
On the one hand, Scripture speaks strongly against gossip. Romans 1:29; 2 Corinthians 12:20 – Both differentiate gossip from slander and condemn it as the result of a depraved mind, unfitting for Christians. 1 Timothy 5:13; 2 Thessalonians 3:11 – Both condemn “busybodies” who “speak about things not proper to mention.”
Or you might only think the story is true (perhaps without good reason), but it turns out to be wrong — hearsay, a rumor, a half-truth (Proverbs 18:13, 17). “The sin of gossip is bearing bad news behind someone's back out of a bad heart.”
The Catechism of the Catholic Church states that one must confess serious sins at least once a year (CCC 1457). One can commit a serious sin without it being a mortal sin.
The Church's teaching on cohabitation is not an “arbitrary” rule. Living together before marriage is a sin because it violates God's commandments and the law of the Church.
The unpardonable sin is blasphemy against the Holy Spirit. Blasphemy includes ridicule and attributing the works of the Holy Spirit to the devil.
They join the long-standing evils of lust, gluttony, avarice, sloth, anger, envy and pride as mortal sins - the gravest kind, which threaten the soul with eternal damnation unless absolved before death through confession or penitence.
How does detraction differ from gossip?
Detraction is disclosing without an objectively valid reason, another's faults and failings to persons who did not know them (cf. CCC 2477). In this case someone has committed an objective fault but it is not generally known. Gossip or detraction consists in revealing that fault to others without a valid reason.
For a valid reception of general absolution, the penitent must be contrite for all his mortal sins and have the resolution to confess, at the earliest opportunity, each of those mortal sins forgiven in general absolution.

It is still considered a mortal sin to miss Mass on a day of obligation without a good reason. The church has always believed that this obligation stems from the Ten Commandments given to Moses, one of which was to “Remember the Sabbath day, to keep it holy.”
– R.L. A: The most direct answer to your question is: no, a personal cannot commit a mortal sin without realizing that it is a mortal sin. The Catechism makes this clear by pointing out that one of the three conditions necessary to commit a mortal sin is “full knowledge.”
The Bible is clear that gossip is a sin and that Christians should refrain from it. Gossip often includes slander, mockery, and denigration. It exposes the gossiper's insecurities as well as their jealousy, envy, and even hatred toward another person.
Malicious talk or gossip is mentioned elsewhere in the Bible, listed along with sins like murder and envy (Romans 1:29), things that should not be practiced or approved (verse 32). Proverbs 25:23, the verse that specifically uses the word backbiting, paints a vivid picture of how people respond to a gossip.
Gossiping, rumors, and badmouthing others is a one-sided way to handle or create conflict and it's incredibly toxic to culture and relationships. “Be the kind of person that stops gossip at the source - it's good for your reputation, and more importantly, it's good for your heart.”
The root cause of gossip is almost always, without fail, jealousy. The more successful you are, the more attractive, the more kind, the more self-assured, the more people will gossip. They do it to try and bring you down.
Gossip, like teasing, can be harmless or, at its other extreme, malicious. As we shall see, much of what is written about the functions of gossip is positive, but gossip as verbal abuse is nonetheless a frequent reality. Verbal abuse generally takes the form of one person's saying something nasty to another person.
Our Ten Commandments booklet shows how the Ninth Commandment “forbids all lying, which includes the sins of slander and gossip. A thief takes physical things that are easily replaced; however, a man's reputation taken by lies, slander or gossip is often never restored.”
Can I receive Communion if I forgot to confess a mortal sin?
If one has not committed any serious sins since his or her last good confession, then it is not necessary to confess before receiving the Holy Eucharist.
There may be some value in that, but there is no place in the Bible where God says that you must confess your sins to a priest. In the 16th century, there was a great movement to get behind the traditions that had built up in the church over the centuries, and to discover what the Bible actually said.
' Ask His forgiveness with all your heart with an act of contrition, and promise Him, 'Afterward I will go to confession. ' You will return to God's grace immediately. You yourself can draw near, as the catechism teaches us, to God's forgiveness, without having a priest at hand.”
Faithful Catholics understand that sex should be saved for your spouse, but sharing a bed with someone you love is another intimate act that should be reserved for your spouse.
The fact that priests will admit cohabiting couples to the Sacrament of Matrimony is no testimony to the fact that the Church looks upon cohabitation as ok.