This would depend heavily on your definition of "penny." Since this is in the US Coins section I will assume you mean American, however there are still variances:
For modern Lincoln cents, from 1982-date each coin weighs 2.5 grams. Therefore 700,000 would weigh 1,750,000 grams, or 3858.09 pounds.
For Indian head cents from 1864-1909, and Lincoln cents from 1909-1982 (excluding 1943 steel cents) each coin weighs 3.11 grams. 700,000 would weigh 2,177,000 grams , or 4799.46 pounds.
For steel Lincoln cents, dated 1943, each coin weighs 2.70 grams, so 700,000 weighs 1,890,000 grams, or 4166.74 pounds
For Flying Eagle Cents (1856-1858) and Indian heads (1859-1864) each coin weighs 4.67 grams, so 700,000 weighs 3,269,000 grams, or 7206.91 pounds.
For Large Cents from 1796-1857 each coin weighs 10.89 grams, so 700,000 weighs 7,623,000 grams, or 16,805.84 pounds.
For Flowing Hair and Liberty Cap Large Cents (1793-1796) each coin weighs 13.48 grams, so 700,000 weighs 9,436,000 grams, or 20,802.82 pounds.
So there you go.
How much does a 2 liter of pennies weigh?
9000 pennies weigh
Depends on whose pennies (which country) and the force of gravity which is not uniform.
One penny weighs 2.5 grams, so 3,500 pennies weigh 8,750 grams.
5,580,000 lbs
60.6172 pounds
167,500 grams
209.439 pounds
1 billion pennies would weigh 5,511,556.55 pounds. The weight of a penny is 2.5 grams
7,142 pennies weighs about 39.4 (39.3635369)pounds.
3.11 grams for pennies made from 1959 to 1982
Approximately 5 lbs