Today is the 84th anniversary of the 7-Eleven chain of convenience stores, and to celebrate, the company is giving away free Slurpee drinks at participating stores in the U.S. and Canada. The free drinks will come in special 7.11-ounce cups.

7-Eleven, Inc. does this promotion every year on July 11. Last year, the company gave away 4.5 million free drinks, the highest number ever. This year, the company is hoping to hit a record of 5 million free Slurpees, a feat company officials anticipate that Twitter followers and Facebook fans can help them achieve.

"We've been serving free Slurpees on July 11 since our 75th birthday in 2002, and it continues to be a hit with customers," said Jesus Delgado-Jenkins, 7-Eleven senior vice president of merchandising, marketing and logistics, in a prepared statement. "Even without the 5 million free Slurpee drinks, July is the biggest month of the year for Slurpee sales. What better drink for the hottest month of the year?"

What's the nutritional value of a Slurpee? Not much. According to Livestrong.com, a Coca-Cola flavored Slurpee has 177 calories, all of which are carbs. Even the company's sugar-free drinks come with some caloric content. A post at WeightDiet1.com reveals that a 16-ounce Sugar-Free Banana Strawberry Crystal Light Slurpee has 80 calories.

So what's the cost to consumers for all of these free Slurpees? As USA Today reports, last year's Slurpee sales went up 38 percent on Free Slurpee Day as consumers got their free drinks and then bought more Slurpees, food, gasoline and other items to go with their free drinks. "Free is magic," says Barry Schwartz, professor of psychology at Swarthmore College, told the paper. "If you offer something for free, people will gladly spend money to get it."

According to 7-Eleven, the company sells an average of almost 13 million Slurpees every month. The drink was introduced in 1966, and has since sold close to 6.5 billion cups, most of which are far larger than today's 7.11-ounce freebies. But that pales in comparison to the company's coffee sales. The chain sells 1 million cups of java every day.

Even though the drinks produce a fair amount of waste (make sure to dispose of your free Slurpee cups responsibly), 7-Eleven is taking steps to become a more environmentally friendly store. The company recently opened 100 new eco-stores in Japan, with LED lighting and rooftop solar panels. Future stores may also include charging stations for electric vehicles.