3. Practice: Chemical reactions are generally classified into five groups, defined below. Balance each equation, using the Gizmo for help.
Combination (or synthesis) - two or more elements combine to form a compound.
Na + O2 → Na2O
2Na + O2 → Na202
La2O3 + H2O → La(OH)3
.
N2O5 + H2O → HNO3
Decomposition - a compound breaks down into elements and/or simpler compounds.
KNO3 → KNO2 + O2
NaN3 → Na + N2
.
NH4NO3 → N2O + H2O
Combustion - a fuel reacts with oxygen to release carbon dioxide, water, and heat.
CH4 + O2 → CO2 + H2O
C3H8 + O2 → CO2 + H2O
C6H12O6 + O2 → CO2 + H2O
Single replacement - an element replaces another element in a compound.
.
KCL + F2 → KF + Cl2
.
Mg + HCl → MgCl2 + H2
Cu + AgNO3 → Cu(NO3)2 + Ag

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.

thats how its supposed to be