LEARNIN 1. Explain the properties of solids, liquids, and gases based on the particle nature of matter
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A solid will retain its shape; the particles are not free to move around. Liquid matter is made of more loosely packed particles. It will take the shape of its container. ... Gaseous matter is composed of particles packed so loosely that it has neither a defined shape nor a defined volume.

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol